The internet as a transmission protocol is robust and redundant. And if it were used as a sort of replacement for the telephone system then that would be enough. But the architecture of the way the internet is today used in practice is far more centralized. If the web worked the way bittorrent does then perhaps your comment would be accurate, but it doesn't, so we have a "web" that is not strong due to its massive interconnectivity but rather weak because each part of it, content-wise, lives in comparative isolation and is easy to cut off (for now).
This legislation isn't about shutting down porn websites, it's about blocking their access at the ISP level. This censorship is circumventable by using a VPN or other such technology. Censorship -> damage, Internet -> routes around damage.
This has nothing to do with cutting off a website from being accessible by removing it from the Internet.
That's an illustration of just how difficult it can be to try to operate a website with the governments of the G8 out to get you. It's something that requires extraordinary efforts for TPB and only works because it's a meta site, if they had to seed every tracker they index they would have died long ago. Moreover, because of the nature of their site and the demographic it's used by it's trivial for them to slap ads on the site and make a lot of money, no matter what.
Compare that to, say, a reporter's personal blog and videos, for example. Especially if they have a family they are going to be much less able to pull the sorts of hijinx that TPB manages. When they're shut down once they will stay shut down and they will more than likely just keep their head down from then on.
