The issue is a few very popular web clients (maybe one that I use) and some mobile mail apps do not have clear implementations of this feature. Until we have an explicit reply-to, I have to modify every single email I am sending to openstack-discuss so it doesn't also send directly (in this case to you) to the sender as well as the OpenStack-Discuss list.
Reply-to-all also doesn't solve this problem, as it (in this case) would add you and openstack-discuss. I agree with Chris on this point. However, as long as we're planning on fixing the reply-to bits for openstack-discuss I'll weather the transitional period.
--Morgan