Not saying he doesn't know what he's doing, just not what I would do. IF he plays great, yeah... what if he plays horribly? There's a better chance of that and I don't see many safeguards for it. Not even saying he's horrible. He could be Rob Johnson or Scott Mitchell... but he could even be Matt Schaub. Now that we know more about Matt Schaub I wouldn't give him that much money either without benchmarks to protect for time missed due to injury.
At this point I don't see much reason to expect so much more from Cassell than Thigpen to lock him into a big time contract.