Fiscally conservative socially liberal conservatives are a dime a dozen. It just doesn't make for good campaign fodder for either side to recognize their existence.
Instapundit links to a WaPo article discussing Rudy's popularity among conservatives. He remarks that he's not too surprised by it, but doesn't address why Rudy gets a pass on most of his socially liberal stands.
To me, it's a pretty simple answer really. Conservatism has never been dominated by the religious right the way liberals have always pictures them to be. Fiscally conservative socially liberal conservatives are a dime a dozen. It just doesn't make for good campaign fodder for either side to recognize their existence. Hey, my ideal candidate is one who is strong on defense, a champion of the balanced budget, and believes that the best government is the smallest government. Show me a candidate like that, and he's got my vote no matter what letter comes after his name.
Or her name for that matter.