Grace, it is not the American work ethic that has changed. It is the American Work that has forced a change. Gone forever is that worker loyalty to their company. This was provoked by the lack of employer loyalty to the worker. Mergers, and acquisitions of American Companies, and the offshore movement of American Companies and jobs is the new worker environment.
Add to that the Employer mandated Employment Contract that is called "AT Will Employment Contract", which basically allows either the employer and employee to leave at will. Of course this benefits the employer as all they have to say is that the employee is no longer with the company.