The New York subway system is the only mass transit system in the US which could stand up to international comparison with a straight face, and NYC is still quite car focused. Sure there are some bike lanes, a few temporary street closures and 14th is closed to private cars now during the day, but still there is no large dedicated pedestrian area in New York of the kind you find in nearly all European cities.
I'd say that's trending into No true Scotsman territory. If it isn't exactly like some elsewhere, it's not true walkability?
To me the definition is very simple: a home is walkable when I can get to my daily & weekly needs by walking. Enough supermarkets, restaurants, assorted shopping, entertainment, bars and plenty of services are all within walking distance.
> even most people who can afford to choose not to own one
I think this is throwing off your walkability definition. A home can be extremely walkable even when the residents own a car. Owning a car in the US is cheap and easy so even if I walk to 95+% of my needs (which I can), it's still nice to own cars for the edge cases. That
This is nowhere near true. Tons of suburbs are perfectly walkable to all kinds of stores and service you could want. I've lived in 6 places in the US and only one of them was not within convenient walking distance of plenty of stores, entertainment and services (and that one was because I chose a fairly rural area at the time).
Yes you can find unwalkable places in the US but you can also find plenty of walkable places if you look for that.