It asks you when you first connect the router. I suspect most people you have contacted are likely to have subconciously (or thoughtlessly) opted in.
If you let me know the URL, I can test from here as I'm on the end of a Sky connection without the opt in blocking so that would confirm if it is that or not.
We had a different problem. They chewed through the fibre cables between our offices to get the fiberglass sheath for their nests. Eventually they ran Ethernet underground because they'd have broken it again in a couple of weeks.
Squirrels act as inductors in DC circuits. Only once though. There's a high current surge that drops to zero as they turn rapidly into a carbon resistor!
The domain above resolves fine with and without the block: http://i.imgur.com/AIqtrxF.png
DNS cache was flushed between each hit.