By obsessing on the percentages of voters they’re missing the meat. The meat is Romney didn’t energize the base, they didn’t come out for him. Add a bunch of voters for him the percentages change. It’s the percentage of AVAILABLE that matters, that shows the people that stayed home.
According to the current Wiki totals, Romney came 5 million votes closer to Obama than McCain did. Romney got slightly more votes than McCain while Obama got a lot less than Obama did in 2008. Most of the former Obama voters simply appeared not to show up, but even if they all showed up for Romney, Romney still would have lost the popular vote narrowly.
Only 3 candidates have ever gotten more votes than Romney, Bush the 2nd time and Obama both times. If anything, we should be looking at what worked in 2004 for us. But even Bush’s 2004 vote total would be well behind Obama’s.
The key to Obama’s wins is that he has turned out a lot more voters than anyone else has ever been able to. That tells me it’s much less a political thing and much more of a cult of personality appeal. Higher turnout from minorities relative to whites seems to have possibly saved him this time, while in 2008 he had enough white support that it really didn’t matter.