Tyler Cowen points us to a study which claims that LA is "on the cusp" of becoming a major walkable city. Two points should be added.
First, the report compares large metropolitan areas. These places have many distinct neighborhoods which are hard to shove into a single category. I have lived in walkable neighborhoods of LA for most of my life.
The reason that large metropolitan areas survive (continue to compete well for labor and capital) is that they offer a variety of opportunities. Yet, analysts are prone to affixing general labels to them -- which inevitably do a poor job of describing the complexity.
Second, large-area averages can mislead. Los Angeles (the urbanized area) has been the densest in the U.S. since before 1990 -- 6,999 persons per square mile in 2010 vs. New York's 5319.This is an overall average and not very useful.
On a related note, Census data show that the LA metropolitan (even larger than the census' urbanized area) is not anywhere near the top as far as walking or bicycling to work go. The champions of walking and bicycling often see these as important parts of their efforts toward reducing commuting by private auto.