Is Kinect eating into Wii sales?

[Reasonable]

1 - you're quite right, without the Kinect launch (and the redesign which I think is too often forgotten BTW) 360 would be a steady third and PS3 would almost certainly have overtaken it by end of 2011

2 - I don't think there is evidence yet 360 is eating into Wii sales in a significant way.  Kinect sold great holiday 2010 yet the Kinect sales made no difference I could see on the Wii seasonal spike - therefore during the Wii's strongest period I saw now major impact.  The post holiday slump is expected for Wii which is more seasonal than the HD consoles.  They all spike during holiday's and they all slump afterwards, but Wii spikes more and slumps more IMHO.

3 - Kinect is still new enough that in the US I believe we're seeing the tail of the launch spike giving the 360 a bit of a boost.  If I'm right over the next 4 weeks the Kinect sales will drop further and stabilize.

4 - At this point I think Kinect may be starting to take a small percentage of Wii sales as a comparable experience attatched to a less seasonal console, but I don't think it's anything major

 

Short version - at best Kinect has taken a few nibbles from the Wii pie, but I don't believe it can be any more than that based on the numbers relative to each consoles holiday performance and normal seasonal trends plus the behaviour of any of th econsoles close to a large release or game changer (such as the PS3 slim, a price cut or in this case Kinect).