Google Maps in Japan seems to be a few steps ahead of Google Maps in America, on a large number of details. I wonder who they have to compete with there.

Yeah, Google Maps in Japan knows a lot more, e.g. it shows actual road widths with delimited sidewalks or it tells you about train platforms and elevators when switching lines. The data is from a third party (ZENRIN, check the bottom of the screen) that provides an insane level of detail. Yahoo uses them, too, but Apple doesn't.

Ah. So it's not a question of Google having to assemble better data to compete with (insert other provider), it's a question of having local agencies that are much more proactive about assembling and maintaining accurate data than Google would be.

I think Yahoo Maps is actually pretty highly regarded there. This is secondhand knowledge though, so take it with a grain of salt