I am not sure whether suburbia is really to blame. People who are not able to drive are likely also unable to climb stairs or to walk a mile to the nearest supermarket and carry the groceries back home.
Also, I would expect that for people in a wheelchair living in areas that do not have a lot of space can be quite difficult.
In terms of accessibility, planned suburban towns are far ahead of older cities that have never been designed with accessibility in mind. Where I live, I can't remember the last time I saw someone in a wheelchair in a supermarket. I guess she wouldn't even be able to get through the aisles because they are too narrow.
Most of the elderly I know who don't have good enough eyesight to pass a driving exam can still walk around ok. My grandmother in Greece was able to do her own errands up until her 80s, for example, even though her eyesight was not good enough to drive. It wasn't a mile to the nearest supermarket, though; that might've been more difficult. In many cities you'll typically find a supermarket within a few blocks, if you live in the city. Here in Copenhagen, I would guess there's a supermarket every 1/4 mile on average.
I don't see many people out in wheelchairs either, and I agree accessibility for them could (and should) be improved. I do see quite a few people with walkers, though.