I think the big difference in cost is that the Japanese worker pays in taxes what the UAW/Detroit companies are paying for retiree pensions and insurance. When you've got that much of a base to spread the cost around, it's not so bad when you compare it to three or four companies laying out the same money from their own pockets. Honda and Nissan aren't paying for their worker's health insurance at home... the government is, and that's one less cost associated with manufacturing cars.
Japanese medical insurance is a very different deal than the comprehensive style in Europe and Canada. Plus I gather from my watching of Japanese video that the care is very different as well. The family is expected to come in and do the laundry on a regular basis over there too. That includes the sheets. Also the Japanese medical insurance has a high deductible and a co pay.
Government pensions everywhere seem to work on the Bismark Tontine model. I am sure Japan is no different. Again, from watching Japanese video, it is considered normal to live with your parents after they retire. Which explains why love hotels are considered acceptable there. Government pension benefits are never generous.
My bank does the health insurance 1/3 to the employee 2/3 to the bank, so can guess the most expensive option, Kaiser, which is closest to the government model, costs the bank $70 per week, or about $1.75 per hour.
So the insurance isn't that big a deal. As a cost, it is huge, but it isn't what is killing the car companies, or providing that big a boon the Japanese.
The big issue is UAW featherbedding. Paying for the no shows. Paying for operating the plant with a full payroll when there are no cars being built.
If the companies could just shut down and re tool, they might survive.
Don't forget one big thing. If the companies get on the government teat, we are paying for the UAW contract too. And the featherbedding.