Hmm. I thought about it, and it doesn't really make sense. I mean, yeah, armor weighs you down, makes you move slower, so you can't evade as good. But wouldn't it make more sense to give a penalty instead? Cmon, a guy with 10 dex and heavy plate isn't gonna be near as evasive as a guy with 30 dex and heavy plate... It just makes more sense that you loose some of your dex bonus to ac for wearing heavier plate, not gain a limited amount.
But then again I guess this goes into the category of "Armor system in DnD blows".
http://forums.ddo.com/showthread.php?t=169064