Did you take into consideration the vast quantity of Bible belt voters, the evangelicals if you will that DID NOT VOTE due Romney being a Mormon into your figures? THAT would make your result moot.
I've commented on that exact subject here at Free Republic many times in the past.
There is no clear statistical evidence that white Conservatives stayed home in 2012.
Romney actually got 1 million more votes than John McCain got in 2008.
Most important:
Obama lost 4.5 million white voters in 2012.
Superficially, a person could conclude that ALL the white voters who stayed home were disillusioned Obama voters.
To my knowledge, no one has ever taken a poll to find out how many Conservatives stayed home in 2012.
I am not saying you are wrong.
But I am saying that the incomplete statistics we do have for 2012 raise a lot of doubt about your conclusion.