You may be right but why am I seeing @gruber's (as an example) replies to devs or bloggers when I'm either following both or not. Keep in mind that I've almost never used the site. I've used the Twitter app for Mac or the iOS version.

The only time I don't see these comments is in my timeline. It may be that it's not supposed to happen but, from what I've seen of these posts, they weren't meant as DMs. When I read them it seemed as something more personal and less comical that exists in a normal Twitter feed from these posters.