It seems to me that if a publication really wants to beat the system, banning users can only work to a certain degree. If you really want to stop them from trying, banning a whole domain seems like a good way to persuade them as long as the bans are temporary.

Disclaimer: I have no idea how effective the user banning methods are, but I assume they can be outsmarted more than domain ban.

HN doesn't have nearly the mass and concomitant crowd problems of Reddit, though.

Not that it banning domains is ideal, but effective implementation is often more important.