Regardless of the precise logic it's no excuse for the policy. Simply hand out a sufficiently difficult PoW to prevent widespread abuse.
I'm quite certain it isn't a generic "datacenter" list though because a given VPN exit that was working will suddenly stop. Meanwhile I have a valid cookie yet that is disregarded.
That is an entirely different matter. They only block (AFAIK) editing which is a scenario where PoW would not be expected to solve the problem. What I was talking about here is IP banning as a (boneheaded) mitigation against high volume scrapers.
I'm quite certain it isn't a generic "datacenter" list though because a given VPN exit that was working will suddenly stop. Meanwhile I have a valid cookie yet that is disregarded.