Ruth (Wheelie Catholic) has got some discussion going about Universal Design and Visitability.
Universal Design is based on the idea that products and environments should be designed in a way to make them usable by as many people as possible without adaption. It’s a very big (and important) idea. Visitability, on the other hand, is a very concrete and specific idea: houses should have a barrier-free entrance and an accessible bathroom.
There’s a wide variation in what people mean when they throw around terms like “barrier-free”, “wheelchair-accessible”, “universal design”, etc. I described on experience along that line in Wheelchair Friendly Homes Nearing Completion.

This seems to be a great debate worthy of sincere evaluation. I used to favor unversal design, but have now modified my ideas to want cities and towns to require all housing built with any fed, state or city funds to be required to have a minimum of visitability in all units, and recommend, and offer incentives to all newly built private housing, including single family, to be visitable.
hehe, I just want to be able to go to all those birthday parties! :)