Another thing to consider is that athletes are competitive (stop the presses). And many professional athletes measure their stature against each other by the size of their deals--the same thing happens in civilian life, too.
If you don't think that players aren't keenly aware of who's making what on their team and around the league, then you're being completely self-delusional. These guys are all conditioned to believe that they're the best basketball players on the planet, and one way they can prove their ability relative to each other is in the size of their contract.
Again, I'm not saying that Rondo won't take a below-value deal, but there are a handful of fairly compelling reasons toward him wanting a max.