I thought House said that he had led his mom to believe that he was with Doctors Without Borders during his prison stint. So, she would have a good reason to believe, based on his lie, that he wouldn't want her to visit him in prison.

Yep, you're totally right, I had the impression that the Doctors Without Borders thing was something he invented during Blythe's visit - but checking the transcript it seems that somehow he communicated that to her at some stage while in prison (hmm - how one wonders). Though I don't know why he bothered really, it's not like they apparently see each other very often, the woman was married three years before bothering to tell him.

Also, just incidentally, wouldn't Blythe have to be a total idiot to believe *House* was off being philanthropic somewhere? Does House honestly think his Mom is going to believe that?

The whole Blythe thing makes my head hurt.