Pardon an anecdote....
While I was out of my apartment a couple months back, one of my flatmates took a couple of CDs I had sitting out and hid them. I found them pretty easily and put them back where they belonged. When tweedle-dumbass got back to the apartment, he pulled the whole, "Where are those CDs?" routine. I told him they were exactly where they belonged, showed them they were in their proper place, and insisted they were there the entire time. I didn't have to repeat that story too many times, before he started to believe it. Point is, people are idiots, and will believe a wide range of utterly absurd lies, provided you are willing to commit to and remain consistant with your story.
Idiot-wife, in this case, is (1) predisposed to believing her husband and (2) has been listening to the lie for at least a couple months. (Of course, she's still an idiot, but not as epic an idiot.)