When you get down to it, McCain is only doing this because of the fact that obama has recently taken a decent lead in polls, gained in battleground states, etc, and mostly because more people feel good about his economic abilities. It's ALSO sort of an attempt to kick obama in the funding nuts, though both have enough to last them till the election. Calling for a stop in fundraising doesn't really affect McCain because he has public funding. Obama stands to lose a lot more money by following McCain's lead. And if Obama DOESN'T suspend campaigning and fundraising, McCain gets to run an add in two weeks making it seem like Obama didn't answer the call and was hypocritical about his desires to end partisan politics.
Risky move, but after hearing Obama's logical response to it, it backfired. McCain didn't plan far enough ahead for that and Obama knocked it out of the park. McCain has been made to look like a cowardly ass from this, especially since people in washington are hinting that they don't need him there.