6 million isn't so high for this type of title.
Then again... Hmmmm... exclusivity kinda hurts it's chances of achieving that.
Scoot it on over to PS and PC and you will hit that 10m in a few hours, or few days at most.
I will be one of those 6 million. But you guys do have a point, it will sell more if it has exposure to more platforms. And the money will be rolling in.