One result from behavioral economics is that people care more about their relative standing to others than the absolute value of the salary. This is why transparency can be a double edged sword. If I think I deserve to be paid more than Joe, as long as I don't actually know how much he's paid I can believe that I'm being paid more. However, once you have transparency and I can see Joe is getting paid more than myself…
i was thinking the same thing - i read about that in Dan Arieli's book Predictably Irrational. I suspect open salaries probably increases them on average.