The NFL wants a structured rookie salary cap to prevent these kinds of contracts, although it's obviously the Raiders fault that they placed a bet on a bad risk. On the back side, though, a structured rookie salary cap would dampen all NFL salaries. There's already a tendency to dump an older player and go with a younger guy. If the owners can sign rookies at a lower salary hit and the players can't negotiate until their first contract is out, only a few players will get offered a second contract unless they're willing to work on the cheap. This is where the anti-trust exemption helps the NFL tremendously. They have a cartel which allows them to collude to keep salaries low by refusing to hire players from another team.
On to JaMarcus, when a #1 pick can't get work as a backup project, he's toxic. Russell's only chance at a stable financial life is gone. He could easily end up like Joe Gillam, the Steelers QB that ended up being a street bum.
You forgot that a given percentage of league revenue is guaranteed to go to player salaries.