Chael's stepping in because he has nothing to lose. He was supposed to be fighting Forrest Griffin and Dana said even with a win, he wouldn't earn a title shot, so why not take your chance on fighting for the title even if its on short notice.
Chael does have something to lose, like getting mangled and beat up.
He was supposed to beat Henderson, but Henderson is coming off wins over Shogun and Fedor, Chael just lost to Anderson at 185, so if he were to beat Jones, I'd argue its a bigger deal than Henderson beating him.
He fought Fedor over a year ago, who is now retired. As fun as that fight was, its not a selling point to the average MMA fan. Chael is a MUCH bigger draw then Dan. If you think that a story line of Jones stepping up to fight the biggest heel in the UFC, and thus saving the card wouldn't be a huge win for him, I don't know what to tell you.
C'mon Henderson hasn't used his wrestling other than in TDD for years now. He's followed the Chuck Liddell school of thought for a long time now in using his olympic caliber wrestling to keep the fight standing and look for the H Bomb
Henderson is nothing like Liddell. Liddell was 10x the striker Dan is, much more diverse. But if you think that Jones wasn't seriously training his TDD and clinch work, again, I don't know what to tell you. I'm quite sure Jones would have looked to keep the fight standing against Chael and work his stand up, which I doubt very seriously he'd have a problem with.
The UFC has helped him build his career, but if he were to lose and take a endorsement/ppv revenue/ championship pay hit, would the other fighters chip in to help him cover that because they got to fight on the card since he was nice enough to take the fight?
He just signed a deal with NIKE, he's going to be OK. He'd also have gotten a rematch right away if he did lose. He has nothing to worry about money wise.
You seriously doubt if Shogun regrets taking the Jones fight on short notice after what Jones did to him and since he hasn't been able to work his way back into a title fight since?
He was on the verge of getting a title shot after the Vera fight. If Machida didn't embarass Bader, Shogun would have gotten it. I cannot for the life of me, knowing what we do about Shogun, picture him regretting a fight.