I never understood what is the motivation for keeping the salaries in industry secret. It seems to reward precisely the wrong kind of behavior!
"What That Idiot Hardcastle at International widgets is on 2 Million, I am worth more than that."
The other reason is that it might expose direct or indirect discrimination.
In academia, even while the salaries are rather meager, at least they are public and equal to everybody (depending only on your position and seniority, according to some public tables). We could very well do with a bit of wage inflation!
(IANAL)