> Don't Reddit and Twitter email you when you get a reply -- or at least have the option to get an email?
Yes, but you would have to check a completely different service to see whether you got any replies. Most people would probably refresh the comments page or click on the notification icon directly in the page.
> With Usenet you had to go check.
Clients could be configured to check for message every X minutes/hours, etc, but just clicking on "Get messages" would show unread messages. And you could easily find replies to your comment(s) since the thread pane would essentially provide an indexed view of the entire thread including every subthread that you could expand/collapse. The other advantage was that you could see new messages in context.
On the other hand, when clicking the notification icon in reddit, you see new messages in isolation and would have to click on the context link to see what they're referring to.
