It actually is not.
John McCain got 97% of the votes that George Bush did in 2004 and 20% more of the vote than George Bush got in 2000. McCain's loss was due to swing voters, not stay-at-home conservatives.
I know that many posters on this forum say that they are staying home and that millions of conservatives will too.
But in reality, conservatives vote for the GOP candidate.
Many - especially here - predicted in 2008 that millions of conservatives would jump ship to third parties.
The libertarian/conservative third parties got 180,000 more votes in 2008 than in 2004, or a lot less than one-fifth of one percent of the electorate.
I'm not staying home. Downticket is far too important. But there's no way in hell I'm voting for Mitt Romney. I don't support statism.
But in reality, conservatives vote for the GOP candidate.
In reality, conservatives can think for themselves. Some will choose Romney and will be stuck with their vote. Others will vote their conscience.