Looking at the scenarios and electoral maps, and then taking into account the massive advantage Obama has in money there is really only one approach for McCain if he wants to win. He has to go national. In small contests like Iowa (which is about as blue as IL at this point, but for argument's sake) Obama can just pulverize McCain because he has much more money and much better ground organization. And if there's one thing Axelrod has proven to be pretty good at it's managing and organizing their resources to take the opponent head on in smaller contests. If Obama spreads out John McCain he can essentially destroy the GOP through attrition.
McCain counters that by pooling everything he has and taking on everything Obama has. The odds are certainly not in McCain's favor, but it's a lot easier to score one big upset than the 13 or so he'll need right now. If McCain can start winning nationally that gives him a bounce everywhere and maybe forces Obama to spend money in states like Wisconsin and Iowa that he shouldn't really have to.