Good point.
Where Romney&co actually campaigned the Republican turnout was up, not down. Just not up enough.
Republican turnout reduced overall only in non-competitive states.
And it leads one to question the effectiveness of the Obama turnout operation. No doubt they limited the damage, but even where they worked the hardest it couldnt match 2008.
You are absolutely right and right after your post I just submitted one that breaks the voter turnout by state.
The best explanation I have seen is that BO's six month barrage of negative ads left swing state voters very jaded, and disgusted with both sides. Remember how Republicans were talking up their early vote turnout, and jeering that BO was wasting resources getting high propensity voters to the polls during early voting? Romney on the other hand was going to let the Republican high propensity voters get themselves to the polls on election day, and worked on low propensity voters during early voting.
Turns out that disgust at the months of ads, mailers and knocks on the door had moved many previously high propensity voters into the low propensity voter category. BO's folks understood the situation, heck, they created it. So they cajoled their turned off (formerly) high propensity voters to vote during early voting. Romney left his (formerly) high propensity voters to show up on their own on Tuesday, and far too few of them did.