Japan is a little different, thanks to the anti-trust win by AMD over Intel in Japan, AMD has traditionally held a lot larger market share in japan then in other countries. That advantage went away somewhat as the terms of the anti-trust ruling were met (and AMD remained uncompetitive in the CPU market), but AMD has held a fairly strong market position in japan it just doesn't have anywhere else.
I'm starting to see some AMD laptop/desktops breaking into the market on the prebuilt, however it seems Dell (unlike HP) is hellbent to avoid offering AMD options, which is bad news for AMD as the vast majority of the business desktop and server markets are dominated by Dell. (Dell does offer some AMD options but they're only in the low end cheep offering, nothing on their high end quality systems)