Actually, if I understand correctly, the hard fork could still have been done even if the funds weren't locked up. It's just that then it might not have been the hacker getting the short end of the stick, but rather whoever was unlucky enough to take their ETH in exchange for some other currency.

The hard fork may have been considered unfair by more people if the funds had not been locked, but the point still stands that if you could get enough of the network to agree with you, you can fork and start over at any block in the past you want.