HTTP 451. I never thought I'd see one of those before. I live in Canada... Not some authoritarian dictatorship. Wonder who blocked it.
This is not true. Your ISP can in theory route the requested address to whatever they want. In the Netherlands TPB is blocked and my ISP returns a 200 status code which shows their blocking landing page. Other ISPs give a 30x redirect to their domain.
Basically the ISP can do a man in the middle attack.