1.26 million Xbox 360s vs. 425,000 Wii U. Seems to me the Wii wouldn't have caught up even if they'd had more time and more inventory.
Also, a lot of people probably bought it for resale since it's the holiday season and the first new console in 6 years. Prices on Ebay are barely above retail though, so demand doesn't actually seem to be outpacing supply by very much.
I would imagine they could have made up the 200K difference their had been more inventory.