The big issue, as many people have pointed out, is that a LOT of workers do not get paid sick leave. People who are living below or even just above the poverty line literally cannot afford to be sick; they're living paycheck to paycheck and don't have any extra money for savings. And, if they can't afford to be sick, then they come in to work and infect others, and the cycle continues.
I don't want to get into yet another H1N1 debate. Frankly, like Gipsy, I can see the benefit of similar legislation separate and apart from the H1N1 issue. But then we get into the health care reform debate.
In any event, in this as in most "developed" nations, employers do have certain obligations to their employees -- for example, to keep us physically safe. As release has pointed out, there has been much necessary legislation passed to promote worker safety.