Oh come one! That's not even close to being true. I live on the west side of Los Angeles, and it's very walkable here. (I believe in those ratings sites that rate walkability from 0 to 100 Santa Monica is something like a 98, just like NYC.) I used to live in Atlanta, and even there certain parts were very walkable at the time (thinking Little 5 Points, for example). San Francisco is totally walkable. Chicago, too. I'd bet most large cities in the US are walkable. Boston was when I lived there.
Anything that holds New York City--by which one presumably means parts of Manhattan and maybe hipster areas of Brooklyn--as a minimal bar would seem to be a rather demanding standard. Very few cities in the world have that kind of density.
>Tiny villages of 20 people can be made walkable.
At some level, this is true. I suppose by some definition, the center of my rural/exurban town is walkable. There are sidewalks, the town green/library/town hall, schools, church, some number of houses, etc. Quite pleasant. But there isn't so much as a restaurant or coffeehouse or store, so while quite pleasant, it probably doesn't fall under what the typical urbanphile would call walkable.