The polls shifted as never before after the Denver debate, because voters saw for themselves that Romney wasn't the villain Obama had made him out to be. Romney has become a man the middle is comfortable with, not an extremist. Independents backed him 51 to 39 percent after the debate, according to polling by NPR, and still do. Romney enjoys a double-digit lead among independents in most polls, and at this point, that's not something Obama can overcome. If you want to know who is winning an election, look at who is winning independents. Obama has lost them.
Romney has won the mainstream. He's done it with convictions like this, from his closing argument in the final debate: "Washington is broken. I know what it takes to get this country back, and will work with good Democrats and good Republicans to do that."
Romney promises to deliver where Obama did not, by working with decent people on both sides of the aisle. Obama can't promise to do the same—because it's clear he doesn't think there are decent people to work with on both sides anymore.
Romney does. That's why he'll win.