Most of the games being developed through the Xtreme Partners program are lower-end, and as such, are being released as valueware through publishers like E-games. Of course, I have NO idea how much money can be made through doing that, but I'm guessing you can't get rich from it (although I know people who make a living from valueware).
I imagine that if you were able to produce a game comparable to top-of-the-line products, it could be released normally through a big publisher.
One thing you consider though is that you are only getting half of what Xtreme Games can squeeze out of the publisher, which is probably going to be somewhere in the 15-30% range, and not much more than you could get on your own. The advantage, though, is that you can get a lot of help, in almost any form you can imagine, and you don't have to go to through the work of finding a publisher. So it's definitely worth looking into.