People make too big a deal over writing disabled characters. Believe it or not, a lot, I think most people with a disability, mental or physical, just... live with it.
I think it's difficult for a lot of people because they don't want to misrepresent the disability or they feel such characters would not fit in the setting they're playing in. For example, a deaf person in a military setting. Unless the person became deaf at some point during the course of the RP itself I think it's difficult for most to imagine that sort of character fitting into a military RP.