Good catch Dewiz. I stand mistaken.
I am not aware of any unwritten rule but I think the reason you don't see many lateral moves without a significant raise is because it just isn't natural. Lateral moves usually arent deserving of much of a pay increase and not too many are going to want to only change the name on the bank account of the check they're cashing. There usually has to be another reason; increased pay, better title, more responsibility, something...or possibly they are aware their days are numbered at their current employment. I don't have an explanation for kaz jumping ship at Iowa but I think we can speculate it was probably that last reason.