The original user on #wordpress (I can't remember who it was) was deleting comments straight out of the database using phpMySql, that's why their `comment_count` wasn't being updated.
Like you said though, it seems that `comment_count` isn't being populated with the comment count on some people's blogs (mine included) in some situations.
Why have you titled this article "hot service in SF, New York, and now London" ? Twitter is a worldwide service just like most things on the internet. Why pick those three cities? London isn't the only place in the UK you know, just like there are more places in the US than San Francisco and New York. Very strange title indeed.