Conceptually I agree with you, Twitter should be able to shut down a botnet like this by simply 'identifying bogus twitter accounts' (aka twitter bots) and 'deleting those accounts en masse.'

The part where it gets weird though is that twitter already has massive botnets which run around in it retweeting things and what not. Which they do not shut down. So is that because they don't want to? Because they can't? or simply because it isn't worth their time? That is still an unresolved question for me.