[cyanoacry]

In this case, Japan's move makes sense. The satellites are placed into an orbit so that they can be seen high in the sky, which is impossible to do for all locations on the earth.

At some point, you need to break up the augmentation systems on a continent/country-wide basis so that you can optimize the satellite orbits to work for you, instead of against you.

Additionally, QZSS seems to be pretty similar to WAAS. I get the feeling it's probably the same sort of system (though I haven't taken a look), so it's likely easy to implement from a GPS chip perspective.