It makes sense. Only Romney supports the agenda of the religious right in all important respects. Better yet, his personal and family life exemplify Christian ideals even if he is not seen by evangelicals to be Christian per se.
My very evangelical church (it leans Pentacostal, even though we reject labels) is very very supportive of Mitt Romney.
Consider the fact that it wasn't long ago that southern Baptists and other 'fundamental' Protestant churches didn't view CATHOLICS as mainstream 'Christian, per se.'
In some parts of Ireland, the Protestants STILL don't view Catholics as 'Christian, per se.'
Personally, I consider Catholics as brothers in Christ, redemption, salvation, life-changing. I love them, and all the good Catholics do in this world, and I was raised as a fairly conservative Baptist.
Likewise, I view Mormons as different, but it's hard to argue against their success in promoting wholesome, hard-working, patriotic Americans.
When I think Mormon, three words come to mind.
Donny and Marie Osmond -- and the Mormon Tabernacle Choir.