Seems like these nodes are the reason that the network keeps forking. Furthermore, even after everybody updates, this presents an obvious attack vector if Evan doesn't add some sort of auto-ban for outdated clients in the future.
Doesnt have to be added, already part of the code. Just have to be configed/turned on.
By each client manually? Why would something so important be off, anyway?
It was/ist off, because before the fork there was no reason to ban any versions.
(And before the fork it was unknown which version (may) make problems.)
To manually turn it on, you would have to recompile from source.
But the normal procedure is that the devs/Evan would release a new version for everbody which nothing change, but having the "ban switch" with the correct version numbers turned on. (And engourage everybody to update once again.)