Obviously, it was NOT the same voters. African Americans were much more motivated to vote for Obama because he is black. Even more important is that conservatives and evangelicals were NOT motivated to vote for either McCain or Romney. McCain was pretty much hopeless, but Romney would have made a much better POTUS than Obama. Had more evangelicals and true conservative showed up to vote for him, he could have won. I still think voter fraud played a significant role in the 2012 election, but fraud only works when the election is close as it was due to the lack of enthusiasm for Romney as a candidate.
A marginal increase in black turnout can help a Democrat in certain states, but can't elect a Republican. Either Reagan voters did nothing for 25 years, or enough blue collar whites flipped in WI, MI and PA.