Here's why: For Romney to score a clean win, he's got to win both the Electoral College AND the popular vote.
Now suppose Romney wins the EC, but loses the popular vote by a sliver, say 50,000 votes. Sure, he'd be president, but he'd be dogged by the popular vote loss. It would be a stone around his neck that he just doesn't need.
Beyond that, there would probably be riots over the popular vote winner (Obama in this scenario) being “denied” his victory.
Best Romney doesn’t believe he has the Mandate of Heaven ~