On those groups the "Reply" link or button itself should be substituted with "Private Message to Sender."

Yes. Or, the "PM" function would be called instead of the "reply" function. 

I can't imagine the purpose of a group where the default amounts to private e-mailing from person to person with minimal sharing with the group. 

Believe it or not, I've seen a few yahoo groups like that.

--
J

Messages are the sole opinion of the author. 

It's dumb to buy smart water.