That is true, but it's largely because of the Evangelical vote. The overall Protestant vote is a little higher than the Catholic. The White mainstream Protestant vote was on par with the White Catholic (possibly even lower). But the Evangelical vote was much more strongly for Romney and that pulled the overall White Protestant vote well above the White Catholic vote.
One thing to bear in mind, though: traditionally, Catholics who never went to church still identified themselves as Catholics. Protestants who tricked away from their churches were, I believe, more likely to describe themselves as not belonging to any religion. Those who identified themselves as Evangelicals were very likely to be frequent churchgoers and very committed believers. I don't know if all this still applies today, but traditionally, comparing Catholics with Protestants or with Evangelicals was a tricky business.