archives.gov has the prior election totals. McCain got 59.6 million roughly, Romney got 58.5 million roughly.
Some suggest that this is due to old Republicans dying off means that they aren’t being replaced by younger Republicans entering the ranks of registered voters.
My real fear is that some stayed home because they didn’t like Romney. Staying home is always a vote for the incumbent effectively.
Democrat losses were greater ~ that's due to the higher mortality rates suffered by blacks (they are about 40% of the effective field strength of democrat voters).
By 2016 the Democrats will be weaker than the Republicans simply because so many more of them will have died, become disabled, or gotten felony convictions.