Both of those RBs being dependent on o-line play doesn't make them equal. Tom Brady would be a poo QB behind a terrible line, and so would Clausen, but that doesn't mean they're worth the same money.
Great point pantherclaw. Acknowledging Williams' production is dependent on line play makes him worth just about as much as guys like Andre Brown.
Which raises the question on why this franchise felt it was so important to spend a ridiculous amount of future money that they will never get back on their efforts to extend either of them.
Obviously, Williams was paid too much without consulting the staff on how they intended to use him. But he was paid according to his ceiling, which is higher than Andre Brown and any RB not named Peterson in the NFL.