Note that it largely correlates to the WalkScore for Boston: http://www.walkscore.com/MA/Boston
I don't know why people don't make walking a bigger deal in where they choose to live in the U.S. I love driving, but
A large part of the reason I've remained in New Hampshire is because my town is extremely walkable from my house, with several cafes, good restaurants, and my work all less than 10 minutes away by foot.
(Of course there are other reasons. I "run" a large victorian-era house and rent spare rooms to friends, living for effectively free. On the other hand, I also don't know why more young professionals don't do that, because the money I save is amazing, and the only downside are more chores, or people problems if you live with friends you end up not liking)