I think two things are at play here with Rasheed...
1) money...and lots of it (lest we forget, that's still a big pile of dough).
2) rest...a now two-week reprieve from basketball.
He came in last season out of shape and he was hurting. Let's not forget this guy wrenched his back late this season - I don't think that will just go away.
I hope this is conjecture (as noted above) and that Rasheed walks away on a high note. His body is beat up and his mental capacity to take a beating is not there. His contract is more valuable than his person, and I hope he walks away and allows the Celtics to use those funds to better the team. If not, I can only believe he's doing it for the money, and though I can't totally blame him, I don't agree with that. We'll be looking at another season of threads here that state, "'Sheed is lazy!" and the like, speaking of the woes of how he should have retired...
What a pity that would be...