Companies are under no obligation to provide any benefits only a pay check for for a service preformed.
In many cases, this is true (union contracts being the major exception); however, it can be argued that it is in the self-interest of the company to ensure that its employees are in good health: When employees are chronically ill - because they don't have and can't afford health coverage - productivity takes a major hit, and if the workforce in general is chronically ill, replacing the "underperforming" employees won't work either, because the replacements are dealing with the same issues.
The solution to a chronically ill workforce is either to provide affordable group benefits (which spread the risks and costs over all of your employees), or to pay your employees enough that they can purchase their own coverage (or pay their own expenses) at market cost. Or you can pay taxes to support a public health plan, which has the advantage of covering everybody (maximum dilution of risk and cost) as well as being not-for-profit (no need to charge more than is necessary to cover outlays and basic overhead).
Then again, there's always outsourcing your labor to countries with surplus populations - such as India and China - so that when chronic illnesses render one set of workers unproductive, there will be plenty of other warm bodies to fill the positions so that the high turnover won't be a problem. While it
could be argued that this option is immoral in so many ways, what's a little immorality when the profit margins are so high?