AmicusE,
I have wondered about that myself. So far, I haven't figured out any way to get rid of the unwanted addresses. I've gotten used to the way the menu opens so I can choose to arrow key up or down the list, or I just keep typing until the address I want is at the top. Either way, it doesn't bother me much any more.
Gary,
The "auto-fill" in the Mail address line works, even if you don't have the address in your Address Book. It works very much like the URL line in Safari where if you start typing a URL that is still in the history, it will attempt to complete the line for you.