good point, but a mining monopoly would destroy the value and hence it's in the self-interest of miners to be diversified. that's an economical self-correcting mechanism on top of this technical mining/reward feedback mechanism.
> And contrary to commonly-repeated assertions, a monopolist can engage in subtle attacks that are hard to detect.
http://hackingdistributed.com/2014/06/16/how-a-mining-monopo...