Interesting - I've worked at US companies with policies just like the one at the top of that page. I had no clue they were illegal. Hard to enforce was obvious though, and I do remember breaking such a policy at least once.
There are policies that the company can't disclose your salary, but I think that people just assume the existence of a (highly illegal) policy that says that you can't discuss your own salary. I make a point of telling anybody who wants to know, and when the specific number is relevant to a conversation (not very often) to not hesitate in giving it.
It's the least I can do for fellow workers, and I know that my salary is no measure of my worth.