Re: the elderly, I think it's also exacerbating the already problematic question of how to care for the increasing number of elderly. There are a lot of elderly who don't really need to be in a nursing home or staffed assisted-living facility, but can't easily live on their own in suburbia because they can't drive. If they were in more urban areas, we might be able to decrease the proportion of the elderly population who need active care, or at least reduce the intensity of care needed.
My mom volunteers for Meals on Wheels (http://en.wikipedia.org/wiki/Meals_on_Wheels), and a lot of the people they deliver to are in decent enough health, but just sort of trapped in suburban apartment complexes. They end up surviving through a mixture of charities like that one, and relatives who drive them around and bring them things. But many end up moving to assisted-living facilities after a bit, even though they don't truly need to live in a staffed facility, because the logistics of living in suburbia without a car are just unworkable, and they either don't know about or can't afford a more walkable area to move to.
Also, because Medicare covers nursing homes for people who can't take care of themselves (considered a medical expense) but not the lower-key assisted-living facilities (considered a residential expense, and more likely to be abused), people who run out of money when living in an assisted-living facility may be forced to move prematurely to a nursing home, if they aren't able to go back to living on their own. That ends up both worse for them and more expensive for the public.
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.