The players don't know how much each other gets, and it's nobody's business except the NRL and the club. And players get paid differently based on how good they are, whether or not they're rep players, etc.
My thoughts on the punishment? Harsh, but they had to do something. The players and fans suffer through no fault of their own, true, but if it means that no other club will try such subterfuge again for fear of being punished like this, then that's a good thing. I just hope the media and the NRL make sure that the players are treated with the respect they deserve - regardless of whether or not they cheated the cap, they were the most dominant club we've seen in years this year.