Matt has weighed in on an HBO forum thread about Halo patches. While he doesn't outright say that there won't be any, he warns everyone to be pretty skeptical:

When you read one of these Bungie is working on a Halo patch stories, feel free to accord it the same respect and credibility you normally bestow on the I have a friend who works with the uncle of a woman who gives pedicures to someone who works at Microsoft, and she says that PC Halo is cancelled stories, or the I went to EB and the guy at the counter told me the release date for the new Bungie game stories.

Wow... EB. That's pretty unreliable. Caveat emptor, everybody.