The company bears far less risk than the employee. The company can easily fire you if it doesn't work out, whereas most employees can't suddenly leave a job that treats them badly.

So employees can ask lots of questions about company financial health, as part of trying to reduce the far larger risk they are taking.

Meanwhile, a company doesn't need to know your salary history to make an informed opinion of whether they want to hire you and for what amount of pay.

Public companies publish quarter results..

According to Forbes: "less than 1 percent of the 27 million businesses in the U.S. are publicly traded on the major exchanges." [1]

[1] http://www.forbes.com/sites/sageworks/2013/05/26/4-things-yo...

That's true but far more than 1% of employees are employed by publicly traded companies. Most of the 27 million businesses have no employees at all--there are only around 5 million businesses with employees.