To the extent that any of these analyses are based on the proposition that Romney got millions fewer votes than McCain, they are provably wrong. What happened is pretty simple: some states and localities take longer to count the votes than others – some big cities are notorious for this, some count absentee ballots slowly, California traditionally counts very slowly, and some of the jurisdictions hit hard by Hurricane Sandy in 2012 were understandably slow getting finalized. But the final numbers are not what was originally available in the immediate aftermath of the election:
In 2004, George W. Bush got 62,039,572 votes vs 59,027,115 for John Kerry.
In 2008, John McCain got 59,950,323 votes vs 69,499,428 for Barack Obama – in other words, McCain lost about 2 million votes from what Bush had received, while Obama gained over 10 million vs Kerry’s total.
In 2012, Mitt Romney got 60,934,407 votes vs 65,918,507 for Obama – a million more votes for Romney than McCain, and 3.5 million fewer for Obama (but still up around 6 million compared to Kerry).
Presumably, some of Bush’s voters in 2004 stayed home in 2008 and 2012, while others switched to Obama or one of many minor third party candidates. But even if we compare Romney to Bush, he’s off by only a little over a million votes, not such an enormous number in an electorate of around 130 million people.