I’m sure that McCain has genuine concern about the economy, and wants the economy to get back on its feet. Whether you agree with his politics or not, he’s still an American, and his own livelihood is strongly tied to the American economy.
I also think that McCain is trying to derail Obama’s recent popularity. The best way to do that (aside from having more popular ideas) is to sweep the carpet from underneath Obama, and force Obama to play on his playing field. By moving the political arena into his own court, he’ll have a better chance of being able to out maneuver Obama.
Obama doesn’t really have a choice in the matter either, since if he doesn’t agree to follow suit, A) he’ll look like an opportunist by exploiting a national crisis for political gain, and B) he’ll look like his commitment to unifying the country is only skin deep. He’ll look like more of a polarizing figure, if he doesn’t play ball.
I know, that if I were McCain, I’d be doing the same thing for political advantage, whether I cared about fixing the economy or not.