In my opinion , the salary issue is culture related.
People in the US pay much attention to their privacy. They don't talk about their salaries with each other in the workplace, or even in their own families. People who work together and do the same job usually don't get paid the same salary, depending on experience, seniority, etc. The employers don't want their employees know what everyone else is making, both in public sector, and more seriously in private sector. Otherwise there will be lots of unhappy people in the workplace.
So people have their privacy by not talking about salaries with each other, and employers have more happy employees because they simply don't know they might be underpaid in comparison with other colleagues. It's a "win-win" situation for everyone. That's why I am not surprised that salary information is often not listed in the job ads.
In my native country, China, salary is not a secret. People talk openly about it. At least it was the case when I was in China until 1986.  It might be changing now, since the country is more modernized and westernized in the last few years, and the gap between the rich and the poor is getting bigger. But generally speaking, in our culture, people are more open talking about money and less sensitive about their privacy.

Qin Tang
Technical Services Librarian
Minnesota Dept. of Transportation Library
MS#155
395 John Ireland Blvd.
St. Paul, MN 55155
651-215-0447
651-297-2354 (fax)
qin.tang@dot.state.mn.us
http://www.dot.state.mn.us/library/