Most major, mainstream MMOGs like Lord of the Rings Online, World of Warcarft, and Everquest have complex interfaces organized in a very flat, context-free structure. Movement, combat and non-combat functions are accomplished via the classic mouse and keyboard control combination. Most functions, especially in regard to combat, are accessed via a string of action functions located on "hot bars" or "skill bars". These functions can either be clicked upon directly with the mouse or bound to specific keyboard keys. Although there are occasional exceptions, each key has only one particular function, regardless of the player's situation within the game. Compare the large number of actions located on skill bars to the number of buttons available on a standard PS3 or Xbox 360 controller and you can easily see where basic interface design decisions just don't correlate well between consoles and PCs. It's not that one interface is better than another; they're just inherently different. In attempting to build a game that works on both PCs and consoles you've got to design to the least common denominator. If the console's controller can't support 50 buttons for different actions or can't accommodate quickly selecting actions via a heads-up-display, then you've got to streamline the experience or make it more context sensitive and intuitive. This act of streamlining an interface can only serve to benefit both console and PC gamers in the long haul.
MMOGs are not new to consoles, but, to date, their implementation can probably be characterized as mediocre. Phantasy Star Online, Everquest Online Adventures, and FFXI, are all examples of MMOGs on consoles. Although it is certainly possible to play these games with a standard console controller, I think most gamers opted for QWERTY keyboards to fully experience the game. If nothing else keyboards were necessary to easily chat with other players. Now that voice chat is a more common option in games, it reduces the necessity of a keyboard. Still, the large number of actions required in an MMOG should be supported by a control pad alone. The MMOG that can successfully use a console's native control pad is going to be more successful than one that requires its players to buy an additional gaming peripheral that isn't conducive to use on a living room couch.
In order to limit the large array of possible actions that can be taken in an MMOG, the actions must be contextually sensitive based on what the player is doing at any given time during the game. For example, if the player is engaged in combat and pushes the X button on a control pad, he might swing his sword in a standard attack. If the player is standing in front of a chest that needs opened and pushes X, the same button also allows the player to open a chest rather than attempt a combat maneuver. This concept of context sensitive button mashing is an old one that's been present in video games for years. It's implementation in MMOGs is less frequent, although not completely absent.
There are certain areas within MMOGs where you can find context sensitive gameplay. In WoW, for example, switching a warrior's stance or a druid's animal form allows players to use the same keyboard keys (1 – 10) for completely different actions. While in a casting form, a druid might use key 2 to cast a healing spell, and while in cat form, the druid might use the same key to initiate an attack. This type of context sensitive gameplay can go a long way to reducing the number of buttons required to complete actions; thus better fitting the limited number of buttons on a console control pad. Taking that concept a step further, if the player was behind an enemy, rather than in front of one, the player could press the same key to initiate a positional attack style, rather than attempting the same attack. The game itself would be smart enough to know what a player was attempting based upon the context of the player's position within the environment and relative to his target.
Age of Conan's "Real Combat" system looks like it's making progressive steps in terms of intuitive, context sensitive combat. In fact, in watching demonstrations of chaining combinations of attacks together, it seems like combat can be executed more intuitively on a console gamepad than with a keyboard-mouse setup. This is probably a good sign since Age of Conan will be available on the Xbox 360 as well as the PC. It will be interesting to see how well the interface works in non-combat situations and how large scale communication (world chat, looking for group chat, etc.) can or will be accomplished.
As MMOGs continue to evolve I think we're going to find the interfaces continually improve, become more streamlined, and more context sensitive. Breaking this interface barrier will not only help to break down the wall between console and PC gaming, but also break down the wall of immersion in our games in general.