As others have pointed out the Wii U's tracking is unusually close to the last known shipped numbers.
Wii U
Nintendo global numbers through June 30: 6.68 million
VGC global numbers through June 28: 6.60 million
Global gap of only 80,000... just slightly above Wii U's weekly sales.
Xbox One
Microsoft global numbers through April 17: 5.0 million
VGC global numbers through Apr 19: 4.1
Gap of around 900,000.
Okay, sure, whatever...