I think you are jumping to a conclusion. More calories..yes. But also more macronutrients across the board -- more to buffer absorption...and a higher volume of liquid. There is a lot going on there and saying the reason is the calories is jumping to a conclusion. Another study would be needed to test if it is the calories, the buffered absorption or some other element that we are overlooking.
Actually I thought WM and IM were both isocaloric and isonitrogenous (e.g., they just added sugar and water or something), but I looked at the paper content more carefully and you are right:
FM and WM were isonitrogenous and WM and IM were isocaloric.
So yes you are right I would like to see then try with also fat-free milk with sugar to get to the same calories to tease out those differences. I know from other studies though that extra calories do cause an increase in AA absorption, but so can extra protein, so yeah, it would be nice to test the contribution of the two independently...
Also I was talking just about milk here, and both fat-free and whole milk have the same amount of casein, but whey and sugar still performs better as a post-exercise drink than just milk, because slow-absorption is a good thing at all other times but not right after a workout, so milk is still good enough but would be even better with no casein, more whey and more sugar.
Post-workout is just a very different situation. It's like for say large amounts of adrenaline and electrical shocks, which are normally not good for your heart, except when you need to restart it in which case they are the best thing to do at that very moment for that particular need.
Fast absorption is good for immediately during a workout...but JUST fast proteins (i.e. Whey) just give you a spike...the real power is unleashed when you have slow proteins to provide a slower, more prolonged elevation of blood AA levels. This is cited left and right through the literature - but for convenience I will just recite what I have posted above.
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2569005
the elevation in blood amino acids was slower and remained elevated for a more prolonged period, providing a more sustained delivery of amino acids for skeletal muscle protein synthesis.
PWO IS different but not THAT much different. The spike of blood AA levels is great for the immediate effects that are caused when coupled with sugar but for a more pronounced benefit you really want the slow proteins in there for the prolonged delivery of AA.
Lets draw a comparison of recovery to a war-torn nation. After a major battle if there is a huge influx of funds it is great for the initial rebuilding process...but if the spike of funds suddenly ends you aren't really seeing a major benefit. If, after a major battle, there is a huge influx of funds followed by a long prolonged period of wealth then the nation can more adequately recover and become stronger than before (supercompensation). (This may not be an airtight analogy but it should help someone else who isn't as good at reading physiology papers.)
I think the problem is that you didn't follow some of those nested references deep enough.
All the evidence you are referring to is just for normal meals with no exercise involved.
For example, in the paper you quote multiple times in your post, the statement is just taken from this [2] paper, specifically:
[2]
http://www.ncbi.nlm.nih.gov/pubmed/12730415which is just about postprandial aminoacid intake, which is a big word for "after a meal". It's just saying after a meal you have more sustained release and uptake with slower absorption, which should be no surprise to you. But again it's completely different for post-workout with its exercised-induced increased uptake, and a timeframe where 'time-released' simply doesn't matter at all and is clearly inferior to fast-release.
For PWO it's not even a matter of spiking, as I mentioned aminoacids are quickly absorbed so you don't get any negative feedback on intake until your muscles are more than saturated and happy, or you completely run out of digested whey, both of which don't happen for a while and when you do you reached your optimal goal anyways.
To use your example of a war-torn nation, you might want to use the most resources at springtime when everything is most-responsive to rebuilding and you have a critically short window of time/opportunity to plant trees etc before the winter comes, and excess money won't be wasted in stupid stuff because there are many concrete things to do and everybody is ready to do them. Later on and throughout the winter, it makes more sense to then have a supply of slow and steady money to keep pipes from freezing etc, and excess funding then would 'spike' and end up in the pockets of corrupt politicians. Or something... analogies...
The equivalent without the analogy is what I mentioned before:
A couple of hours after the end of your exercise and PWO drink you can certainly go back to slow-absorption protein, carbs etc and be better for it, but immediately post-workout they would be taking away from the much more needed fast absorption ones.
And in terms of rehydration:
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2569005
The ability of milk to effectively act as a rehydration beverage likely relates to the composition of milk. Milk naturally has high concentrations of electrolytes (133 mg Na+ and 431 mg K+ in a 250 mL serving) which aid in fluid retention when consumed. Another factor that has been speculated to contribute to the ability of milk to be an effective post-exercise rehydration beverage is the rate at which it empties from the stomach [22]. Energy dense fluids empty from the stomach much more slowly, leading to a slower absorption into the circulation [23]. This slower absorption attenuates the large fluctuations in plasma osmolality that can occur with consumption of large volumes of water or sports drinks. Subsequently, the large fluctuations in osmolality (decreased osmolality) [caused by sports drinks, NOT milk] would result in increased clearance rates by the kidneys, similar to those observed by Shirreffs et al [22], resulting in large increases in urine output.
Rehydration is a completely unrelated issue from fast or slow absorption of protein and protein synthesis.
And even if we were talking about rehydration problems, the additional clearing of excess water from a sport drink (which was never what we were discussing, unless sport drinks contained whey too for example), the issue would be only one of efficiency given a limit on how much you can drink after losing too much fluids. If you can afford to drink an extra sip of a sport drink or water+salt+sugar, then you are probably better off, since being able to use that extra water for filtration is generally an advantage.
Again, regardless of side discussions about efficient water retention, all evidence on post-workout drinks clearly and conclusively shows the opposite of what you are claiming. Fast-absorption is ideal, slow-absorption is sub-optimal. That's why whole milk is not as good as just whey+sugar right after workout, while something like cheese (mostly casein and fat) is better throughout the day and especially night for total protein absorption and synthesis.
If you found even a single paper showing specifically any advantage of slower protein release and slower digestion immediately post-exercise, that would be a big plus for your current position, but again if you follow any of the links and studies and papers you cited so far, it's never about post-exercise, and again all the literature I have ever seen specifically about post-exercise measurements always shows clearly that faster absorption is better.
