If it's for real, I respect him for the decision. But the truth is that he's leading in most polls and so his suspending the campaign will force Obama to do so as well and thus lessen the time for Obama to campaign to garner more voters.
So, I think he's doing this to generate some more credibility on the economy and shrink Obama's overall lead by appearing more concerned about the economy. McCain is hoping this concern will translate into becoming more respected in the economic arena, thus leading to better polling.
As if McCain/Obama can take a breath right now without considering the implications on the election...