Equally likely they notice the thundering herd of non-subscribers accessing a select few articles through a particular hole in their subscription wall. Surely can't be that hard for them to track.

The problem for me is always which ones? If I were to dig through my browsing history and plot a frequency/frecency list of news-ish sites I visit, I don't think I'd see a small few dominate the list. I wouldn't mind throwing a couple bucks a month at the sites at or near the top, but I can't justify giving each of them even $5/mo, and certainly not the $10-$30/mo most publications charge for memberships. I just don't get that much value out of each one.

I'm still a big proponent of a micropayments system where my browser can automatically send a single- or double-digit amount of cents to the publisher (with my permission, of course) when I read an article. But I have no expectation of something like that gaining traction.