I think they did this by providing a consistent format (both data format and by enforcing limits), a central view and a usable api. RSS/ATOM just didn't get this right. Twitter forces people to get their message across in a small amount of characters. RSS/ATOM again is inconsistent in mainly due to it trying to be a portable medium (reading full stories in a reader). I guess the twitter model is more natural?
Perhaps there is a place for adopting a twitter based format for future rss feeds and making viewers around this.
I personally like the idea of sites having a dedicated twitter account to post updates to, I don't use rss feeds but like getting information via twitter.