Mmmm...I don't have a problem with PC's knowing the rules per se, but I will say this.
#1: It makes it harder for newbies. The easiest thing in the world to say to someone just starting off with D&D is: "Tell me what you want to do, and I'll translate it into mechanics." In that respect, "I trip him," becaomes something you imagine doing and want to do. In 3e, you could know the mechanics or not and it wouldn't matter. In 4e, you HAVE to know the mechanics.
#2: It puts an extra step in between Imagination and Result. You have to translate the effect into mechanics, and then back out of mechanics, to achieve what you imagine. In many ways, this ties what you imagine to what you can possibly have mechanics to accomplish. You don't think out of the box so much because the box is defined for you (as your powers).
Keen insights, I like where this thinking is taking me.