I think "on a shared workstation" means it was an electronic document and not a physical sealed envelope.
Fair point, and that sounds dicier. 'Round these parts (California), that employee might have a case for wrongful termination. But maybe not; snooping around corporate computer systems, even if the door is unlocked, just doesn't look good.
In the other case, though, now that I think about it, even if I had signed a contract that said my salary was confidential, surely that's only an agreement between me and the company? Would I really be violating such a clause if I disclosed my salary to another agent of the same company? It just doesn't seem like there's anything management can really do to prevent this sort of thing.
Seems like the only thing that keeps people from discussing this sort of thing more is the fear that someone's feeling are going to be hurt -- either theirs or yours -- if it turns out there's a big salary discrepancy.