No, people who have tried SL and left unimpressed are making an judgement informed by their experience. To say that they had little clue about what goes on there simply means that Linden and the cabal of initiates in the know have done a piss poor job in exposing "what goes on there" in a simple, attractive and easy to use fashion.
The rest of your post was interesting - I hadn't thought of SL's possible uses by the disabled community.
Nothing ever becomes real until it is experienced. - John Keats