I do agree. It depends very much on to whom you're confroted with at the check-in counter. My girlfriend was recently flying MUC-JFK and she had the cheapest ticket possible (W) and went accidentally to the Business check-in but anyway she was treated very nicely and they didn't send her back.
So of course there are rules and terms the staff has to abide of but I would not say that they are making no exceptions... You can be a *G and anyway treated like an animal or you can only be *S and enjoy a great service it doesn't matter with which member airline.
Just try it!