Why is their a news piece about NSMB being fastest game to 15 million?

[Khuutra]

Seece said:

I know The Source is a big fan of the Wii and not so much the HD, but MW2 is A game, and it reached 15 million in 8 weeks, much faster than NSMB

VGChartz lists games according to separate SKUs. It's the fastest single SKU to ever hit 15 million.

That's all there is.