A couple of things.
PC isn't that niche in Japan. They have far more shelf space devoted to PC games than the US. Far more obscure games get PC releases. There are even stores that specialize entirely in adult PC software. When I bought a keyboard a few months ago they had specialized Final Fantasy and other mmorpg keyboards and a big Razer section at the store.
I can also see the 3DS scoring lower as almost everyone already has one. It is unbelievable how many I see on trains. A few per car at least. And, I would imagine Famitsu readers would definitely already have one.
360 at 10% is surprising, but maybe it is getting cheap enough that people are willing to take a chance in order to check out some of the exclusives. Used games for the 360 are also much cheaper than the PS3 counterparts.