I think the idea that forced brevity is an important component of microblogging is mistaken. Low friction to post, minimal formatting, and (optionally) collapsed long posts in feeds all encourage short posts without requiring them.
It might have served more of a purpose when Twitter launched because people weren't in the habit of short text posts at the time, and because Twitter supported posting via SMS.
There is a chance that I just don't get microblogging. I've always felt that short character limits encourage people to make bad points that resonate emotionally but fall apart when thought through, and to yell at people they disagree with rather than being thoughtful.