So I'm not surprised by this. Xbox 360 users tend to be a bit more hard core than Wii owners.
According to survey data compiled by Nielsen, the Xbox 360 dominated the charts, while the ubiquitously successful Wii came in dead last by a huge margin, ranking below the PS2, original Xbox and GameCube.
The chart is tracking the percent of console owners who use their gaming hardware on a regular basis. Everyone and their dog owns a Wii by this point, but very few actually play them consistently, according to Nielsen's findings.
Too bad you can't monetize usage as easily as a console/game sale.