According to the Huffington Post/AOL crowd, "Obama may be responsible. Essentially, the argument is that Obama's election has created such collective inspiration that it has changed the thinking and the behavior of would-be criminals." Sounds a little ethereal if you ask me.
Now for my school of thought, which, as it happens, is based on known facts. Since Obama got elected, sales of guns and ammo have gone through the roof. In fact, it is nearly impossible to buy ammo in some areas as they just cannot make it fast enough. Now, since so many people are arming themselves - and are angry enough to be prepared to use them - criminals are having second thoughts about committing crimes, knowing it is likely they will be shot by their proposed victim.
Of course, feel free to believe whichever school of thought appeals to you, or develop your own. It could simply be that, since Obama has kept the nation broke, no one has anything left to steal.