Hi,
I just tested, and indeed you are right, you can't point specto towards a google groups page (but why would you want to? It's a mailing list, the whole point is of subscribing to it to receive updates in the mail! :)
My guess is that Google chose to reject any user agent that is not a web browser; I just tried pointing wget at it, and it gave a 403 error (but browsers like epiphany work fine). I doubt it's something we can fix.