To a lot of people sell = popularity.
With windows 7, it was no question to its popularity, so no one questioned it sells numbers.
But windows 8 isn't as popular as windows 7.
So Microsoft's sells numbers showing it sold 60 million are under question.
How many were sold directly to customers
How many were sold to oems
How many did Ballmer himself buy? (Joking of course)
These are questions people want to know, because they paint a more actuate picture of windows 8 popularity from Microsoft own mouth.
To me, they have no reason to lie. If they've been lying all this time, wouldn't someone have caught them by now?