Ah wars of semantics. I consider Kinect a half-platform really, going by how its performing.
Half new platform, half huge accessory. So its half balance board half Wii.
Going by that, and seperating the demographics buying Kinect into Kinect you get:
X percent buying Kinect as an add-on to their console - and this figure is lower than the figures of people buying Wii Balance Board as an add on to Wii. If 40% of Kinect purchasers are existing X360 owners, we're talking 1.6m vs. 2.6m or something (off the top of my head)
Y percent buying Kinect X360 as a new console - and this figure is lower than the figures buying Wii, DS, PS2, etc at launch. If 60% of Kinect users bought it and X360 to play new games, were taling 2.4m for Kinect-sold consoles in six weeks vs. 2.9m for Wii in six weeks, or whatever the actual figures are.
However, when you take X & Y together, Kinect outperforms Balance Board, or Wii at their launches. But I do think its mathematically disingenious to pretend that there aren't two demographics at work here, rather than a more unified demographic smaller demographic for Wii at launch (the GC fan), and Wii Balance Board (women / expanded audience). If Nintendo had liscenced out Wii controllers to Sony for PS2 in 2006, "Wii" would have been higher too, same is true if "Wii" was sold as an add on to GC in addition to Wii in 2006 in addition to its own package, which is comparable to what Microsoft has done, minus the marginal clock-speed upgrade from GC to Wii.