I’m curious; I think everybody is curious things they consider outside the norm. But I never ask.
The way I feel is that, for people with disabilities, dealing with the disability is a big part of their life (bigger or smaller, of course, depending on the disability). But the people I’ve known with disabilities are complete people, and no matter how servere the disability, it’s only a part of the person. So, if I’m not in a position to know the person as a person, it’s pretty shallow of me, not to mention (IMO) rude, to ask about the part that stands out.
Another thing is that, if you’re friends with someone with a disability, you stop noticing it. I’ve asked friends to do things that were completely impossible for them, because the fact they used a wheelchair went completely off my radar. Since they’re eminently aware that the chair sticks out, they always like it when that happens. Bastards never do what I asked them to, though. 