I get you. But also:
- Email doesn't retain context very well. If I dig back through my email I might have all of the emails in a thread, or maybe not.
- Likewise, I can't send someone a link to a previous emailed conversation so it makes for poor documentation. I can forward an individual email, but not the comment in context.
- Email is not easy to index or post up for reference. You can't link it from a wiki or other documentation for example.
An internal mailing list with archiving would solve many of these issues and might be the best option, but it's a slightly different solution.