Twitter's USP lies in the 140 characters. The character limit forces users not only to choose their words correctly, but also makes them state things concisely, cutting down on all the crap and crib that nobody cares about. I can go on and on, saying the same stuff in different words because a blog entry would let me do that. But twitter its different. If I have to say this on twitter it will probably be like
Twitter works coz its 140 char limit forces us to say things concisely.
No cribs/rants. Focus is on facts. It makes us more articulate.