Reply All should also honor Reply-To: IMHO.
Example:
Suppose that Secretary Suzy sends Jack an e-mail, with Reply-To: set to Boss Bob, and there is a Cc: to Amy.
From: Secretary Suzy Reply To: Bob Boss To: Jack Cc: Amy
Jack hits Reply All, and the mail should go To: Boss Bob in lieu of Secretary Suzy, yet preserve the Cc: Amy:
From: Jack To: Bob Boss Cc: Amy
I.e. Reply-To: just means "in any form of replying, substitute this address for the sender".
I believe this interpretation is correct.
Ben.