1) To prevent hiring people "below 40k" you just make it so you dont pass H1B's for "below 40k".

2) International employee does not normally know something like this exists, and I assure you the Government website is not made with such a goal in mind. Not to mention that even in that case the salaries provided here have all kinds of inexact data (because it doesnt show stock compensation)

3) Any country can make the immigration policy they desire. Having this information public denotes a second-class citizen measure. This would not be acceptable if, for example, employees from other states in the US had to do this to "protect the state's jobs and make sure everyone gets a fair salary".