Absolutely.
Having employees not discuss salary is all about the employer having more power/control, and the employees having less.
I've always thought it's a little like an adult giving candy to a child and then say "Now, don't tell anyone I gave you this!".
Why doesn't the adult want anyone to know about the candy exchange? Because they benefit from keeping in concealed.
EDIT: I also think this is a generational thing. Everyone I know over 40 wouldn't dare talk about their salary, or how much they paid for their house, etc. Everyone I know under 30 will happily talk about it to anyone and everyone. Give it a few more decades, and this will be the norm.