I can understand how needing greater bandwidth can cut off a minority of miners.. but how can it concentrate it into the hands off just the few? If you look at bandwidth usage statistics aren't a majority of the people that mine bitcoin currently considered high bandwidth already? Therefore this "centralization" simply means into the hands of what already is a majority which should theoretically get even more dispersed the more high bandwidth connections are available right? Or is some extremely powerful bandwidth connection able to eliminate "normal" high bandwidth users?
So your biggest fear is that alternative solutions to the block size limit won't be made? In other words what the other guy mentioned bitcoin clearing houses? How does that help decentralization?
Read up on "high frequency trading".
What you are thinking of as "high bandwidth" is godawfully slow compared to, say, a composite cable less than half a mile long of parallel optic fibres, or whatever the currently state of the art fastests fattest most-direct short-hop direct link is. Basically it could become infeasible to mine anywhere else than in the mining district of the mining colony in the arctic or in antarctica, with the final showdown being between those two (or actual best, since they might not have cheap power to go along with cheap cooling, so maybe Iceland as the "artic" one), with only one pole being able to win since the other is too far away to compete with it. Maybe a see-saw between them as each increases hashing-power to try to make its hemisphere the world's mining capital instead of the other hemisphere...
-MarkM-