scanned my 2011 email and analyzed my activity. It makes sense to me. I subscribe to MANY e-lists that generate daily emails - I don't reply to those.
Also - I send quite a few blast emails myself - to SCSD staff - and I don't expect any reply. They are news, information items.
Monday is the busiest day - no surprise...
I send the most emails in the morning, before 7 am - no surprise either.
I still rely on email, although I use iChat, Skype and Twitter as well.