Your graph on the front page may be inaccurate. This page says Wii U sales (without this week I think) are at 2.55mil. Your graph seems to be just a little below that. Were there adjustments in previous weeks? It's probably not worth changing it until Nintendo releases their figures though.
Regardless, Wii U is certainly slowing down and they will not hit their projections. Interestingly, however, Wii U (even with these numbers which are perhaps too low) has already outsold the 360 through to March. Goes to show that launching first doesn't pay dividends, and indeed that first console out often struggles at launch.
Come the end of March I see Wii U at 3-3.5mil
I have the exact data (now including this week of jan 19th) from VGC weekly charts. I think that graph is missing updates.