This is simply not true. It has nothing to do with at-will employment. It is state law. Some states require consideration separate from salary, some say continu

This is simply not true. It has nothing to do with at-will employment. It is state law. Some states require consideration separate from salary, some say continued employment is sufficient consideration. 49 out of 50 states recognize the doctrine of at-will employment. Only Montana uses just-cause instead (just like the rest of the developed world coincidentally).