It has to do with the "bounce" the bat gives the ball - they're trying to make aluminum/composite bats play more like wood bats for safety.
I knew about the changes at the college and high school level (partially thanks to this board - KLav18 and others) but didn't realize it was being pushed down to middle school kids.
Overall I don't think it's a big deal or bad thing, except that it forces parents/teams to buy new (and fairly expensive) bats, and of course I happen to be at the point when the boys are just getting to the big fields so it's a double-whammy.
