The importance of interface in any piece of software or any tool, for that matter, is often paramount in terms of its usefulness. The success of the iPod, for example, does not so much stem from its number of features as there are other mp3 players which boast more bells, rather it is a highly thought out user interface to which its success is more likely owed.
However, we often do not think about the interface in terms of the differences on the part of the user. There is an unspoken assumption, it seems, that all users are somehow equal in terms of physical structure that can be guessed from the design of end products. We often see mice, keyboards, and game pads coming in one basic size or accessibility.
Though a market around software and hardware for those with disabilities does exist, the specifics of these issues in massively multi-player environments have only started to be addressed. As the MMO worlds continue to evolve (I won’t say “mature” as I believe they are still in their infancy), groups such as Virtual Ability and AbleGamers are taking on important facilitating positions to help those who wish to partake in this growth of communication.