They do; but the proposed system would do the same thing in an entirely non-centralized way.

This would be a good thing because as it is now, there are multi-coins pools that will switch their users' hashing power to other chains depending on how profitable coins are. The concern is that large mining pools have a lot of combined hashing power and some dishonest ones could consider switching that power to specific coins not based on the revenue potential but for other reasons (51% attacks and the like).