You might be right that these plugins block cookies or the javascript that informs you that you've hit your limit.

They've tried to make the paywall as permeable as possible. For instance, if you follow a link from twitter or facebook it wouldn't count. But if you went to the NYTimes directly, it would.

The idea is to tax heavy users and those who have more money than time.

It's far from conclusive, but this trend is a disturbing one.