One wrong hit can end a proven player's carreer just as easily. I haven't heard anyone who doesn't think rookies are paid comparatively too much.
When Ronnie Brown is guaranteed more money than Brian Westbrook and hasn't proven himself, that could be a big problem. Let's just say (not that this will ever happen), that Ronnie Brown turns out to be a bust. You've already given him a $19 million signing bonus, so if you cut him, you take a $16 million hit on your cap. So you have to stick with him and he messes up your backfield for a few years. That's why some teams are picking so high every year. Their picks turn out to be busts. Limiting rookie salaries would ease this concern. I agree with this, because for every Peyton Manning, there is a Ryan Leaf