[thalur]

The thing that jumps out at me is your first question: the majority of the actions I get from e-mail come in the text of the email and are external to the mail client (implement this feature, fix this bug) rather than part of it (reply with an answer, accept meeting request).

I think the reason why email works for this is that somehow email "comes to me" whereas everything else I have to consciously "go to it" to check it. I recognise that some of this is habit, some of it is how the email client is integrated into the computer (outlook at work, mail on my iphone) so that it presents new stuff to me directly, and some of it is that it presents a single place to check rather than having to hit refresh on a bunch of webpages to see if anything has changed on each.