Hi John Boy,
Around here, I've seen a mixed bag. My home group is like yours. You have to be a member of the group to do either coffee or chair. In fact, you'll have to fight the guy who does coffee because he will not give up that position to anyone.
But I've also chaired and did coffee for other groups that didn't have those requirements. I let the secretary be the one who makes the call. What happens most of the time is the secretary will ask for volunteers. Then I'll get with the secretary and ask then if you have to be a home group member. Usually if they ask for volunteers, they don't have that rule. And it usually works out best for either way a group does it. The groups that keep it closed usually do that because they have enough volunteers. The groups that are open, usually don't have enough help to get all the jobs done.
For my home group, I would be horrified if chairman would be open to non-home-grouup members. It would be the end of a great home group because the non-members would turn it into "NA" in a heartbeat because of the big amount of treatment center folks that come to our meetings. But I also know that if you ask for volunteers to chair, only the folks that volunteer get chosen. There is no such thing as "you have to chair" because you are a home group member.
I've been taught like you, if I refuse a reasonbable request, I should tell my sponsor. And at first, I was like you too. I needed to be told what to do. Even when I volunteer to help today, I show up and say "Tell me what you want me to do to help" because I do well with a little bit of direction.