You are looking at differences between developers, but try pretending for a while that they are all the same, moderately qualified to adapt to any environment. I'm pretty sure that you would still see roughly the same distribution, since all environments are not created equal, and neither are the different positions inside those environments.

The stagnant bog of billing hours to captive (e.g. internal) customers for example does not lend itself very well to a toolmaking microsingularity. Bimodality of pay is at least as much about the task as it about the one one executing.

There is of course still a lot of correlation between ability and high value positions, but that's a natural consequence of matchmaking: both high value positions and high value developers get disproportional choice relative to their lesser peers.