Urls where fixed to 22, then 23, lately 24 chars. It's the length of the actual shortened url.

I've been working with people helping social media for a bit, and one common issue in preparing a list of tweets to schedule is making sure the length is ok. So you end up with silly xls files where you have a url column, a text column, etc. and weird formulas to compute the size.

I think Twitter just wants to simplify the life. You can send 140 chars of text/comment. Mentions, urls, images, etc. are not counted because normal people aren't counting like that.

He was asking why URLs ARE still being counted as part of the length – Twitter seems to have excluded everything except for those. Your reply demonstrates how arbitrary that distinction is :)

From the blog, replies aren't broadcasted. Only new tweets that use "@" are broadcasted.

What they mean is that .@ isn't getting removed -- by default your replies won't be broadcast to everyone (same rules apply as always) -- but since you no longer see the leading @mentions, you physically cannot do .@ on the tweet. The right way to do it going forward will be a retweet on your own tweet.