I've read somewhere that Google extensively uses mailing lists internally. They’re probably using the same codebase for their internal mailing lists, and the storage costs effectively nothing to them.
Google: nah.
Honestly I shouldn't even suggest that, it will probably get google groups closed in a whim.
I have trouble imagining what a vim/emacs user group would be: either some sort of nonstop abusive flamewar or some kind of kumbaya group you can only join if you can prove you're on a dangerously high dose of lithium.
Also groups that trade baking recipes in org-mode format plus vim macros so they can share the fun.