Would this be related to the claim that Americans are never poor, just temporarily embarrassed millionaires? Only people at the top would have nothing to be embarrassed about, while everybody else would love to tell you how much they make once their ship has come in.

Hmm I would say that Americans may be wary of revealing their own personal salary, but that there's very open discussion of typical wages for any given kind of position in the US, and it's not considered taboo to complain about being offered a salary below your expectations.