From the comments
Steve S writes:
Steve Entin at the National Center for Policy Analysis has written on the very issue of the subsidies vs the tax exclusion. His conclusion:
Adding the subsidies for premiums and cost sharing, the family getting the health exchange policy would receive a total subsidy of $17,400, while the family receiving employer-based insurance would receive a total subsidy of $4,143.
That is a huge differential. The whole piece is here: http://www.ncpa.org/pdfs/Health-Insurance-Exchange-Subsidies-Create-Inequities.pdf
File under "Not a political equilibrium."