A lot of time I was curious. Does interviewer (and company) have the right to ask any kind of questions and make their choices (BEFORE HIRING) based on age, sex, race, family content, salary history, ethnic origin, etc. How may I refuse to give away that very sensitive information? How may I be sure that I am dealing with employer, at all? What does "Equal opportunity member" logo that I frequently see in North American logos?
Here in the USA - Equal Opportunity Employer is supposed to mean that they don't discriminate on a number of factors. Salary history is not one of them. This EOE business is a result of government legislation. IMO, the laws are hard to enforce. So the employers are on the honor system. Things are better than they used to be.