California voters desired the ballot initiative concept to allow the people to place issues on the ballot that wouldn't get there through the normal legislative process. Initiatives allow the will of the people to be expressed if the legislature is unwilling to express that will.
California passed Proposition 8 and it modified the California constitution. The people's will was expressed and the Supreme Court of California (SCOCA) upheld Prop 8 because it amended the California constitution.
Then plaintiffs brought suit against the State of California in federal district court and argued that Prop 8 was unconstitutional under the US Constitution. A single judge, Justice Vaughn Walker, found the law unconstitutional because, as he divined, the majority of Californians could only have voted for such a law because of their animus toward gays. It is not clear how he could know the motives of the voters. Even though it is not the judge's role, nor is it possible, to determine the motive of the people, Judge Walker did just that. It is similar to when others say that the only reason anybody opposes President Obama's policies is because of racism. There is no way for those doing the judging of other's motives to know this, but apparently they are sufficiently confident in their judging of other's hearts to make legislative and judicial decisions based on it. So in this way, these oracles might just as easily conclude that your vote can be thrown out at the ballot box if you voted for someone other than Obama because the only reason you would cast such a vote is because you have animus toward a black man which means you are a racist and racist's votes should not be counted because that is not a proper basis upon which to cast a vote. This is essentially what Judge Walker's ruling based on his unfounded augury did. (It will be interesting to see whether those opposed to bigamy, polygamy, incestuous marriage, open marriage, et al. will argue something other than what Walker identified as "not a proper basis on which to legislate," that is, "moral disapproval, without any other asserted state interest" and "animus" towards these groups.) To Walker's defense, even if there were compelling societal reasons to support Prop 8, the defense of those reasons may have been so weak or ineffectual that Walker may have had no recourse but to conclude that animus was the only reason that remained.
As a matter of process, it is the Governor's job to defend the laws of the state. This is why you often see court cases with the Governor's name as one of the parties in the suit. The state's Attorney General enters the court on behalf of the people and defends the law that the people through an initiative or the legislature has enacted. However, in California both Gov. Schwarzenegger and Brown refused to do their duty and defend the people's will in court. They decided that their feelings on the matter overruled the majority vote of the people.
If the Governor decides to not enter the court to defend the laws that the people have willed via the democratic process, he/she is in effect nullifying the law and ignoring the initiative process because the people automatically lose the case because nobody shows up to defend their side. (This is called a default judgment and is similar to when an arresting officer does not show up at a traffic violation court hearing, the case is forfeited, or lost, by the party that does not appear in court.) In this case, Gov. Schwarzenegger and Brown both refused to represent the people of California in court as they were required to do.
Fortunately, it just so happens that California has a law that allows somebody else to defend a proposition if the elected officials refuse to. The SCOCA has affirmed this process wherein the proposition supporters are able to come forward to defend the law if the elected representatives won't and acknowledged that the whole point of an initiative is to allow the people to overrule representatives that are unwilling to legislate the people's will by allowing the people to legislate from the ballot box.
Because a gay couple brought the case and since they are the ones harmed by Prop 8 they have standing. However, the appeal to the Ninth Circuit and ultimately on to the SCOTUS were brought by the supporters of Prop 8 because California governor did not step forward to defend the law. As discussed earlier, the private supporters have standing in California because of their law that allows supporters to defend the proposition when the Governor/AG refuses to. But there is no federal allowance for surrogate defense when the state government refuses to defend its own laws. It was for this reason that the SCOTUS decided that the Prop 8 supporters had no standing and that the last legitimate action, whether correct or not, was the decision of the federal district court.
So who are the winners? Gay marriage supporters and by extension any other type of marriage supporters. The loser? The initiative process.