My gut tells me insurers are more than likely to migrate to the Marketplaces as well, since they have a government subsidy waiting for them to pocket. I thought this explanation about the family rate was helpful in understanding the calculations:
After tax credits, bronze premiums for a family of four may be below those for a single individual. This occurs because the tax credit is calculated as the difference between the cost of the second lowest cost silver plan premium and the maximum payment amount determined by income. Because premiums for older individuals and families are higher than those for younger individuals, tax credits are larger for older individuals and families. Therefore, using tax credits to purchase a bronze plan may yield lower bronze premiums for older individuals and families than for younger individuals.Here's a link to the individual cities around the state, or "rating areas," and the prices shown above for those cities. Ezra Klein has a whole list of great questions answered here. I would check it out, it'll probably clear up any nagging questions you might have. It did for me.
Finally, the Milwaukee Journal Sentinel made their own graph: