alt Hacker NewsEmployment ain't guaranteed either, so I'm not sure that guarantee is worth much.
And you can be pretty sure that many workers would walk if the extra goodies they are accustomed to but which ain't guaranteed were to be withdrawn. Assuming the competition still provides them.
There are good reasons for companies to provide those benefits. And they most definitely are part of their total compensation. When a study does not take this into account, their results are not valid.