Ironically overturning DOMA was the gays states overturning Federal law. And overturning the CA referendum was the opposite at the same time by the same court.
Dont expect any consistent legal principles in the courts decisions, its mainly justice Kennedy ruling the country now.
Technically, Prop 8 still lives, it is just being stayed by Walker's court. None of the merits of the case were decided by the Supreme Court, only the technicality of who had standing to defend it.