But maybe
for them it's a feature. It keeps the microblog content in a particular shape, like daily chat but not too-serious, long-term-valuable content.
Clearly there's a market for both. And maybe they could even be... confederated? That is, it might be possible to combine several sources in your stream, and accept identities across servers for easy commenting. Heh, this all awfully reminds me of the stuff that was already built in early 2000s, with RSS/Atom, the original OpenID, and no huge corporations interested in taking over these small potatoes.