I don't much about Montreal's rules, but I do know that the articles and video have been pulled. I think it's reasonable to assume that if this was the normal practice in Montreal, a statement to that effect would have been made, instead of an attempt to silence criticism.
Chances are UFC did try to pull a fast one. But was it even acted upon? Did GSP make a legitimate 170 regardless of the loophole? Was there a panic wherein something fishy was said in confidence that ultimately never came to fruition? There are too many variables at play here.
If UFC tried to accommodate a fighter with 'new' rules, then I agree it's not right. You can't ask one fighter to make weight for a title fight at one event and then extend another some loophole at the next event. But I'm torn... had one fighter not made the 170 mark, this wouldn't have been a title fight... was this just the lesser of two evils? Would fans have been all for this deviation were it made openly and Nick was given more than an hour's notice? There's a lot to ask ourselves.