This isn't true. In the posted numbers, there aren't any major discrepancies between people doing the same job. But imagine if you saw two programmers with roughly the same background and experience with a $20k+ difference in salary. The reason you don't see that is precisely because the salaries are public.
Your error is assuming that the same formula would be used if the salaries weren't public. The employer is forced to use a simple, consistent formula. They would be under no such pressure if all salaries were secret.
Your error is assuming that the same formula would be used if the salaries weren't public. The employer is forced to use a simple, consistent formula. They would be under no such pressure if all salaries were secret.