I believe that in their guidelines it states because a gay couple could not marry the would get domestic partner benefits, BUT it also evidently states that if gay marriage becomes law in any state they operate in gay domestic praters in that state must marry to continue benefits. But because a man and woman can marry they cannot receive benefits as domestic partners.
It has evidently been worded in a way that they have not had to provide domestic partner benefits for all couples, the wording is also specific enough to now stop gay domestic partner benefits in the state of MN, as they are no longer prohibited from marrying. I believe gay domestic benefits will continue to be available in FL and AZ since those states do not recognize gay marriage.