Mrs Carbo-
"retarded" can be/is used as an insult here also. Most of the time it is said like "You're such a reeetard".
I prefer to think of myself as having some medical and physical challenges rather than being disabled, although I do realize that "disabled" does not mean the same as "unabled".
You're certainly correct about there being such differences within the english language. This is complicated even more in the written form when you take away body language, facial expression and intonational changes.