"My campaign is about getting this economy back on track" is a quintessentially anodyne, standard thing for a politician to say.
Why did it sound so terribly jarring when McCain said it? Because he had just spiraled off of an extended riff of complaint about John Lewis's "outrageous" comments, about Bill Ayers, about Obama's negative advertising during a Dallas vs. Arizona football game he watched, etc., etc. McCain's focus couldn't have seemed farther from the economy right then. It was just a patently weird thing to say at that moment -- like seeing somebody adamantly insisting he's wearing green when he's standing right in front of you in red clothes.
There's a problem of consistency with McCain that I don't think he'll ever resolve. His supporters and elements within his campaign are agitating to get nasty, but he doesn't seem able to fully embrace that choice, damn the torpedoes. But neither does he fully reject it. So you get a herky-jerky, forward-and-reverse performance.