Here are a few sales datas about Xbox games in Japan. (Feb 22 2002 - Jun 27 2004)
Halo sold 76,963
DOA3 sold 216,825
DOA Xtreme Beach Volleyball sold 127,576
Thoses are the Top 3 of the best selling titles in japan on Xbox.
On a side note i found funny the claim about Capcom denying MS offers... Because the last "Xbox only" game that Capcom shipped was Circus Drive (Group S Challenge in the US) an another Gran Turismo Killer, Capcom sold 3,900 copies of it in Japan... And 830(!) copies of it in the US.
So, there's no need to precise that Capcom is no more interested in MS offers.
edit: Today, you can find ANY Xbox games in some Japanase videogame store (in Akihabara) for less than 5$... If, of course the store keeps on selling Xbox games.
MS have to gather more support in Japan for their Xenon or else, it will be bis repetita.