I may be missing something, since I haven't tried all of them, but it seems that none of those platforms can be called an "asynchronous IRC"? That's the appeal of Twitter for me:
Oh, and like on IRC, technically minded people tend to gravitate to the platform. Is there anything except Twitter that would offer the same features? There used to be identi.ca, but seems like it's gone now.
"We are on the verge: Today our program proved Fermat's next-to-last theorem." -- Epigrams in Programming, ACM SIGPLAN Sept. 1982