It's the same in Finland. Tax rates are fairly easy to discover for anyone. And based off that you can get a very good idea of their earnings. In practice I've never met or spoken to anyone who has gone out their way to do this. It's normally just the tabloids outing the salaries of politicians and celebrities once a year.
One recruiter said that he'll find out my salary from my tax return when I said I didn't want to disclose it to him. By the way, I think the actual income is public knowledge, not the tax rate.
I expect he/she was calling got bluff.