Are casual gamers the ones who buy devices in the first 60 days after launch, though? Most "casual" gamers probably still aren't really sure exactly what a Kinect is or what it does. (I know I'm not...)
Casual gamers are driven by trends and early adopters. A lot of these people know what Kinect is because their "nerd friend Alphonso" won't stop talking about how cool it is. Don't knock the early adopter crowd just because they are small; while they may be that, their extended social circle is generally large enough to sway even the mainstream numbers.