"The actual bandwidth used by a 300M customer and a 1000M customer is usually the same. The provider's upstream contracts would not change much if they put every one of their customers on 1000M."

Correct. I have a gig/gig symmetrical connection and a family of four information-devouring people. In the last 30 days we used 1 TB of data... which is to say, an average of just over 3Mb/s. We probably peaked at about 600Mb/s a few times.