(1) Wrong use case. This is like... 95% of the time for people unhappy with the Surface.
(2) Faulty units. The unlucky 5%. Estimated. Could be the OP, since he mentions exchanges. (Although there are the unreasonably anal ones for minor defects like screen-bleed-you-can't-see-except-under-extreme-conditions, so those people don't count.)
(3) But the numbers don't lie, either. 4-plus out of 5 stars for all user review aggregates, both generations. Whatever loud complaining goes on in certain quarters, even here, the majority of buyers are happy with it.