>I would imagine that the tendency to answer surveys is equally distributed.

But then maybe the sample isn't. The companies which were trying to become certified partners or whatever they were called that year, may be more responsive to those surveys, hoping to earn more brownie points. And from the two examples I saw I'd say that they are also more willing to push Microsoft's latest and greatest in their own shops. So some percentage would go to more answers coming from those who are already sold on the flagship product.

That may just be the little finger on one side of the scales.