I don't think noreply is about not wanting people to respond to your messages. It is rather a solution for all the garbage you get back when sending out email to thousands of people. You will get many many mailer deamon mails for people who typed their addresses wrong or whose mailbox is full (yes, there are still webhosts that have a 20 MB limit apparently). Filtering all this stuff takes lots of effort and seems like a bad thing to spent time on when you can just use noreply and include a "Have questions? Email us at service@example.com" line.