If several countries, distribute across various continents, have managed to put in place three-strikes and six-strikes (not that I think it's good), it means that the one and foremost knee-jerking argument saying "You can't do anything about DDoS because: [X] It's technically not realist" is gone. Technically now ISPs could throttle the bandwith (or even disallow net access) to zombies boxen used in DDoS attacks in a…
Most ISPs charge for bandwidth. Outside of governmental coercion, is there any incentive for them to do this?