For me, making out that the ball didn't go in and not telling the ref it did is no different than cheating. I can't see any difference between what the Bristol City players did and Maradonna with his "hand of god". I would be more than just a bit pissed if the Swindon players pulled a stunt like that - I'd prefer to lose than win by cheating.
This sounds puritanical and am not sure how many would agree when actually in the situation - but I couldn't agree with you more.