I agree this stinks. However, the ruling is spot on.

The state of Michigan voted to ban gay marriage. This means that gay couples were to be denied any benefits that stem from a martial union. Insurance is one of those benefits that can only be availed by a spouse, a common-law partner or relative and since Michigan has a law in place where two people of the same sex cannot be spouses (or even common-law partners) the court was right to interpret that the amendment forbade such benefits for gay partners.