Have you ever thought about why other microblogging sites have faded away while Twitter continues to swallow every one of its clones?
Oh, BTW, do you know those Twitter clones or sites that offer(ed) similar services?
It is mainly due to the lack passion and drive on the part of the owners of the above mentioned sites. Of course, finance also played a major role in Twitter's success.
I believe tumblr.com arrive a little before to Twitter but look at where it is now?