I have known about ASMI for several years.
I think it is important to note that it is not the actual pitch counts that we disagree upon, just the frequency of when they "pitch".
Take a closer for a MLB team, he may be called upon to pitch almost every day as long as he only pitches a little bit. His frequency is quicker than a starter because he keeps a low pitch count and can recover quicker.
I see my sons situation as being very similar because he doesn't pitch a lot in games or in practice sessions. He can rebound much quicker because he isn't getting as fatigued as someone who has high pitch counts.
I am not sure on the exactness of it but I think that the LL organization has adopted a pitch count frequency based off of what they believe is safe. Under those guidelines they allow no rest period for pitchers who pitch like 25 or less pitches in a game. What they are worried about is pitchers who pitch a lot in a game and then play in another league or game and pitch a lot again while they are fatigued.
I am not sure of if any studies have been done on recovery time in pitchers arms and how much recovery time they need according to how much they throw. I do know this- When my son is allowed to pitch an inning or two in a game and then come back and pitch again an hour or two later he almost always picks up range of motion, control and velocity the second time he pitches.
I do also know this and I do not fully know why, but it is interesting- When my sons arm starts to get sore from throwing if he goes and does batting practice and then resumes throwing afterwards the pain goes away quicker rather than just having him rest. I don't know if it is the increased blood flow or if his arm was just cramping up or what but motion and movement seems to always help speed up the recovery process.