When I go through their publicly available profile and look at their tweets, I can see tweets that did not appear in my timeline as public replies usually do. I can only assume these are DM's.
EDIT: Am I somehow mistaken? I've seen them not only on well-known people but on friends as well when I asked them about this.
If you follow me and I @-reply someone who you do not follow then that tweet will appear in my public timeline but it will not appear in your home view.
I've followed both and have seen them in their individual profiles which is why I always chose to use SMS for things that weren't meant to be public. Any public @reply or retweet I should see and have seen. If these are DM's I shouldn't see any part of the conversation.
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.
