We hear this a lot and somehow feel it's true but there are no reliable metrics and little verifiable data so ultimately it's just talk.
It certainly seems like there is an element of truth to the numbers, but I think they tend to be both drastically overstated (there are fewer cases where there is a drastic difference and/or the difference doesn't matter) and drastically understated (there are cases where one developer can accomplish something that another simply can't, making the difference infinite).
So much time is spent trying to point out and quantify this difference, often in an implicitly self-congratulatory manner, and I think it would be better off spending that energy on:
1) Figuring out how to quantify developer skill, or at least come up with roughly accurate ways to determine whether or not a developer is appropriate for a given task. We, as an industry, are pretty bad at this.
2) Figure out ways to move more developers from the B & C camps into the A camp, insofar as we can actually identify those distinct camps.