http://www.reuters.com/article/latestCrisis/idUSN21171999 1943: The War Labor Board rules that a wage freeze designed to keep inflation in check during World War II does not apply to health insurance benefits, creating an incentive for employers to provide health insurance as a way to build worker loyalty.
http://books.google.com/books?id=UDWZpSUR1aMC&pg=PA100... As a result of wage freezes in the World War II period, group health insurance became an important component of collective bargaining...
Also, it's silly to say that only employers can afford health insurance. Obviously the employer considers the total cost of employing you, including salary, healthcare, FISA taxes, etc. If employers stopped providing health insurance, it's likely that wages would increase (approximately) by the cost of that insurance. Then you'd have that money available.