I was reading about it on CNN.com. The commentators there seemed to feel that it was unlikely that the ruling would go to the Supreme Court simply because it's so narrow. The court didn't rule that gay marriage itself is a right, etc, but ruled that the specific case of California, where the rights were taken away by ballot vote, is unconstitutional. Because the ruling was so narrow and affects only California's case, they said it was unlikely that the Supreme Court would take it, since the Supreme Court is supposed to be concerned with rulings that affect the country rather than just one state.
Essentially, since the court was careful not to overreach, their decision may well stand up much better.