Matt Yglesias mentions another Romney advantage I didn't touch on Thursday night: He has an explicit "delegate strategy" and is executing it pretty well. He had the highest delegate count coming into today and will pick up many more with his overwhelming victory in Nevada, which has more delegates up for grabs than the higher-profile South Carolina contest. As Matt says: "At the end of the day, you need delegates to win. A strategy to win delegates seems like a smart strategy."
One other bit of savviness: Every political junkie in the world was watching cable this afternoon waiting for the results of the Democratic caucuses to roll in. While they were waiting, they got to see Romney's beaming mug over and over again, as he basked in the glow of his relatively uncontested Nevada victory. (The GOP went several hours earlier today in Nevada.) Meanwhile, a lot of people will be out on the town tonight when we get GOP results from South Carolina. So Romney may get a slightly larger boost than you might expect from Nevada, while the winner of South Carolina may get a slightly smaller one.