What I’m describing is that a gay married couple can move to idaho and sue. Yes they can do this in boston too, but California has more people and has the 9th circuit so they will be more willing to try that over there. Also with more and more states recognizing gay marriage at some point they’ll feel more confident with their case to the supremes.
The legal challenge is not only more likely due to a second state having this ruling, and not only because the state is populous, but also because this state allows residents of other states to wed there without regard to the laws of the state in which they reside.
This means a homosexual couple who lives in Idaho could “marry” California and then challenge their home state in court when their “marriage” is not recognized.