People need to remember that MMORPG's aren't the only MMO games out there. Sure they are the dominant archetype among mmo's, but successes have been made of others too, many of which are more suitable for consoles.
An MMOFPS like Planetside would suit console's perfectly in my opinion - easy enough to control using a standard console controller, and a good mix of action / twitch and persistent elements. Some console games are halfway there, they provide persistent elements in having ranks / xp for characters and allow weapons and skills etc to be selected accordingly ala COD4 or BF:BC.
The main difference is the lack of persistent elements affecting the environment of scenarios the players are playing. They are still playing standard multiplayer games but with added persistent elements on their characters. Part of me wonders why few people are bothering to try anying mmo-like on consoles, considering the potential money to be made. I can see no real technological reason full blown mmo's can't be done on consoles more often, so it makes me think developers simply think the market isn't there.
It could be that developers think most console gamers would be totally against paying monthly for the privelage to play a game. Big mmo's with high server and support costs maybe won't exist until people are more used to the idea of paying monthly for a game.
Someone will crack it at some point though, and make millions(billions) when they do.