As far as I know, it is a well known "fact" that casuals only bought wii sports for the wii, and then left the system on the shelf, never buying any game afterwards, except maybe Wii fit. Now, it's also said that few hardcores bough the system, and most of those sold the system after playing only wii sports and though it was crap and sold the system, or they bought maybe a few Nintendo first party games, so who bought the leftovers?
I mean, 869.06 divided by 99.84 is 8.71. In other words, there is an average of 8.71 games sold per wii (a few of the games are on store shelves, but so are a few of the systems). So if "core" games only bought a few games, if more than just buying the system with wii sports and then not buying anymore, and casual gamers bought just a few games too, then who bought all those games to get the average to 8.71?