Let's look at what I can expect if I screw someone over with the lowest possible salary:
* An employee who can justify doing the bare minimum it takes to get the job done, because after all, he's being paid the bare minimum
* Low morale. Can I not expect the individual to bitch about how poorly the company treats its employees?
* High turnover / no loyalty. How much money am I going to waste bringing people up to speed, only to see them hop to the next job as soon as possible? How can I expect to retain valuable employees when I don't treat them as valuable from the start?
It's a poorly run business that screws over it's employees, customers, and / or partners just because it can. I like to think most good business people recognize that that sort of approach does not yield the best results over the long term.
Frankly, I have no concerns about revealing salary requirements or providing salary history. If a company doesn't treat me fairly during negotiations that's a huge signal that it's not the sort of company I want to work for.