While I think constitutionally you're right, the problem is that one state changing the definition of marriage creates major havoc on the others. Thus it needs to be rejected at the national level with a constitutional amendment.
Not only do we have to worry about states creating problems for other states, but we also have federal judges making up laws and misapplying equal protection clauses. Leaving it to the states is a recipe for the success of those that want to redefine sodomy as marriage.
I know. I know. But the broad argument really needs to be addressed, not a specific case. If we voted on a states right to define marriage, then all bases can be covered in a yes vote..including polygamy, brother and sister etc. Now, if gay marriage is approved (I said if), next thing you know three dudes and a monkey are suing for their right to be married. Get it?
In the end, I think the state does have the right to define marriage. Now as far as one state voting one way and another state voting another way all I can say is some states have the death penalty and other don’t. I know most states traditionally recognize marriages from other states but who says that’s an absolute?
The bottom line is all this should remain in the voters hands....not like abortion was handled.