Oh, did they create a new messaging protocol that is universally accessible, redundant and easy to use?
Something the vast majority of people couldn't care less about. Twitter has, in effect, created a new messaging protocol, in the broadest sense of it. It's accessible on your computer, your phone, even your TV if you try hard enough. It's integrated with hundreds of apps and sites. Technically speaking it isn't doing anything particularly amazing (although the sheer scale they deal with is), but that's not really the point.
A massively decentralised protocol would not exactly be the model of reliability, either. I'm not even sure how that could possibly work in a service like Twitter.
It would probably work like an IRC network. A network might involve hundreds of servers, but you only notice which server another person is using when there's a netsplit. Split users can reconnect using another server and rejoin the channel with only a slight interruption.
An IRC-styled Twitter would need some sort of synchronization service to handle twitsplits.
Something the vast majority of people couldn't care less about. Twitter has, in effect, created a new messaging protocol, in the broadest sense of it. It's accessible on your computer, your phone, even your TV if you try hard enough. It's integrated with hundreds of apps and sites. Technically speaking it isn't doing anything particularly amazing (although the sheer scale they deal with is), but that's not really the point.