That list actually highlights the issue with MMOs on the Xbox 360:
- Age of Conan: "development hell", though still possible
- All Points Bulletin: not confirmed for any consoles yet (check this at gamescom last week)
- Champions Online: may actually come to 360
- CrimeCraft: not confirmed for any consoles yet
- Huxley: "development hell", looking less and less likely
- Kingdom Under Fire II: may come out, and will be on 360, but we've not seen the MMO part yet, and it's still got a vague 2010 release date
- Marvel MMOG & Marvel Universe Online (same thing: cancelled by Microsoft, parts became Champions Online
- Stargate Worlds: not confirmed for any consoles
- The Secret World: as Age of Conan (same developer, except even PC version is still rather vague).
That's not really a great list in the end. There are likely various reasons behind these issues, including development costs, but I'm sure Microsoft's tight grip on Xbox Live is part of the problem. Of course, console MMOs in general are an issue, as we have yet to see one on the PS3 either, though DC Universe is getting there, and SOE have a couple more on the way, along with Square Enix's FFXIV, of course (which itself may end up on 360, once they are able to negotiate the Live issues).