It's only a temporary reprieve. The SC decides not to rule for all sorts of reasons. They usually state that a case is weak for some legal reason. I think they are just timing a decision -- partly waiting for a case on which they can rule definitively and with confidence, and partly waiting for new SC nominees to be seated, with the obvious assumption that they will be of a conservative bent, so that the gay marriage decision they finally hand down will be a clear majority, not the 5-4 they've been getting lately on a lot of hot-button issues.
Still, it's always difficult to predict what the SC will do with a case that would seem to be partly a states' rights issue. Conservative justices tend to support states' rights more than liberal justices. They will be obliged to consider if supporting states' rights is what the Constitution requires or if there is an overriding, public interest concern that is stronger, as with public school integration. The argument of the segregationists was states' rights, that they had the right to segregate and call it "separate but equal" when in fact it was blatant discrimination.
The gay marriage situation is a little different (many, I know, would argue very different, but that's another discussion). I suspect that the SC is hoping that, while it is waiting for the case worthy of consideration, the Massachusetts legislature will legislate gay marriage out of existence, so that the worthy case will never happen. The worthy case will be, I suspect, the first time a Massachusetts same sex married couple moves to another state and demands the marriage be honored by that state (as most states do by law or custom honor each other's marriages now).
If that happens and the SC agrees to hear the case -- and the SC is by then full of conservative justices -- it's really impossible to predict what would happen. Conservative courts often rule very narrowly in provocative cases, so the SC might simply rule that, in the interest of states' rights, states both have the right to recognize and not recognize these same-sex marriages. That is, the SC might not pronounce on the broader issue of the legality of a state extending marriage to cover same-sex unions and whether this exceeds what states have a right to do. Or they might. They might or might not rule on the issue of equal treatment, which many advocates of gay marriage see as central to the argument -- that gays are treated unequally under the law by being denied marriage rights.
Or something else I haven't thought of might happen. Like the SC might make some pronouncement, pro or con, concerning "separate but equal" arrangements like California's domestic partnership law.
Here in California we continue to move forward with our domestic partner law which, as of January 1, 2005, will grant DPs many of the rights and most of the responsibilities of married people. DPs will have to obtain divorces if they want to split, and CA's community property laws will apply if there is no prenuptial agreement. DPs will also have all the inheritance rights and assumed property rights of married people. What DPs will still not have is the right to file a joint tax return with the state of CA.
So, yes, I'm glad they chose not to rule, but I would in no way interpret that as support of the Massachusetts law. It's just a decision not to get involved at this point, most likely with the hope that they never will have to get involved.