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.

Wikipedia maintains a quite exhaustive list of them to prevent spam and they also block vpn IPs as soon as they're found.

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.