Comment 191 for bug 52667

As you see you would have "expectations" how it should behave.
I have different ;)
I feel that two separate options are better as it is perfectly clear what will be done - you don't have to guess. And they do what they say - All is All, List is List.

As for usability of reply to all in "mailing list context" - I wanted this exactly for the case you have mentioned - to be able to reply to people that are not subscribed.