That is right. The hierarchical nature of this setting makes it impossible to be fully open, unless you truly are the most uninteresting person on the planet. If not, open and indiscriminate sharing is going to be a potential liability. Some things in life are very useful to know, and I believe being deliberate about what you share about yourself with whom is one of them.
I expect to accomplish my tasks. I can be friendly, polite and humorous but you don't need to know anything about how I live.
The main factor is a boss or supervisor can act on their judgement of an employee and employees do not have the same leverage.