A story in Technorati yesterday revealed findings that almost half of all Twitter followers are bots. That can hold conversations. And no, I don't mean yesterday's @sweden account either. I mean actual bots, as opposed to real people.
Brands use the bots to increase their followers in the same way you have to "Like," a brand on Facebook to engage with their shiny new app. It's clever. And the article makes the point that no real value comes from having a a huge follower count, especially one where half is made up of software.