ISPs don't currently have any incentive to block Bitcoin. BitTorrent uses a lot of expensive bandwidth. ISPs block it to save money and reduce the number of expensive legal complaints that they receive, not because they're evil. Bitcoin is very low-bandwidth, and no one is going to send a complaint to your ISP just because you're running a Bitcoin node. If ISPs did block Bitcoin, they'd be pissing off their customers without getting anything in return for it.

If Bitcoin is blocked (which is very easy), the blocked users would just need to use Tor.