I don't disagree with Professor Volokh's documentation of this phenomenon per se. But oddly enough, it seems to cut both ways. When Maryland's high court upheld our state's prohibition of gay marriage, it also relied on the increasing legislative protection for gay couples -- but to the opposite effect. It claimed that these policies proved that homosexuals did not need additional protections by the courts -- that they were now fully capable of participating equally in the democratic arena (Conaway v. Deane, 401 Md. 219, 286-90 (Md. Ct. App. 2007)). The enactment of policy protections for gay couples, in this case, served as a barrier to further reform. It made the slope "stickier." Justice Scalia has made similar (albeit unsuccessful) arguments in his own dissents in gay rights cases, using the legislative accomplishments of the gay rights lobby to undermine the case for legal intervention.
The problem seems to be adequately encapsulated by Jack Balkin in his wonderful article, "What Brown Teaches us about Constitutional Theory":
In general, courts will protect minorities only after minorities have shown a fair degree of clout in the political process. If they are truly politically powerless, courts may not even recognize their grievances; and if they have just enough influence to get on the political radar screen, courts will usually dismiss their claims with a wave of the hand. Conversely, as a reform movement for minority rights gains prominence through political protest and legislative lobbying, courts will increasingly pay attention to minority rights and take their claims more seriously." [Jack Balkin, What Brown Teaches us about Constitutional Theory, 90 Va. L. Rev. 1531, 1552 (2004)]
As Massachusetts and California appear to demonstrate, some demonstration of political power -- showing that attitudes towards homosexuals have "liberalized", in this case -- appears to be necessary in order to "grease the slope" towards gay marriage. But, as Maryland demonstrates, this is a move fraught with peril: courts can just as easily use legislative gains as an excuse to hamper or delay pleas for judicial reform -- to make the slope "stickier."
There is irony to this, of course: disempowered groups shouldn't have to demonstrate political power in order to see their rights vindicated (though, it should be said, this is precisely what Critical Legal Theorists predict we should see in such cases). If limiting marriage to heterosexual couples is a violation of gay rights, it is just as much so when they are a totally marginalized class as it is when they are only somewhat reviled. But if we are going to demand political clout as a precondition for rights, it's perverse to turn around and use their new-found (limited) influence in legislatures as an excuse to deny them those same rights. Once again, either the marriage equality is a right or it isn't. If it is, then the fact that they can't secure it legislatively is proof that -- regardless of how successful they are on other priorities -- they hold insufficient political power to vindicate all of their rights in that arena. If it isn't, then courts should say so and explain why.
But what we're seeing right now is absurd. At best, it appears that there is a very narrow "band" of relative political inclusion upon which minority groups can launch claims for judicial protection: too little inclusion and the courts won't pay attention, too much and they'll claim their intervention is unnecessary. At worse, it appears that the rules of the game change so as to permanently preclude meaningful judicial protection for minority groups -- any amount of political power (lots, some, none) can be used as a reason to reject their claims.
Ultimately, as in most cases where the facts lead to indeterminate legal outcomes, my suspicion is that the amount of power possessed by a given minority group will likely be interpreted in a way that is most amenable to judicial policy preferences. Judges who want to increase protections of gays and lesbians will use their increased influence as proof that discrimination against them is archaic, while judges who oppose such reform will use that same evidence as an argument against viewing gays and lesbians as marginalized at all.