[taylodl]

You failed to mention the context of that government incentive - World War II. And the incentive you're referring to was put in place by the War Labor Board in 1942, during FDR's presidency. http://en.wikipedia.org/wiki/War_Labor_Board

[dnautics]

you'd think that with the end of the war, the incentive would have been removed.

[taylodl]

It was. But perqs proved popular with employers because their value were hidden from the employees. Thus large employers could use their negotiating power to procure health insurance for their employees at a relatively low cost. They were effectively getting cheaper labor, a huge competitive advantage. The ruse was up once health insurance costs started skyrocketing.