Our initial reaction to this data was that Nielsen is high on pot, but we can kinda understand what caused the Wii's disappointing placement on the list -- 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. Meanwhile, there's only a handful of GameCubes out there that haven't been converted into lunchboxes, and their owners apparently use them a bit more frequently.
If you're looking for a more straightforward breakdown of console usage, Nielsen also figured the overall usage totals for each console. That chart's posted after the jump. (You'll find it slightly above the deluge of inflammatory comments.)