It's an absurd idea that has just enough basis in fact to keep it cropping up every six months or so.
I think that the reasons for the continuing life in this rumour are twofold.
First, your average PC doofus is uncomfortable with the idea of a computer that doesn't use the same architecture as his pathetic beige box. He can handle the idea of a non-Windoze OS, but it has to run on Intel or AMD to stay within his psychological comfort zone.
Second, I think that the slightly more knowledgeable PC type who runs a case modded anodized purple PC with a window in the side and sparkly doodads secretly dreams of being able to run OS X on his pride and joy. But he can't quite bend his tiny mind around the idea that running OS X requires buying a whole different kind of computer that won't run his favorite games, and owes nothing to Bill Gates.
So, that's my explanation for the continuing popularity of the rumour - it's a wish fulfillment fantasy for the various layers of PC doofuses.
Cheers :-> Bill