I was reading an interesting piece today that was speculating that because of how this decision was phrased, it may not make it to the supreme court: it doesn't say that gays have a constitutional right to marry, only that it's unconstitutional for a public referendum to remove the rights of any group.
Had it found that gays had a right to marry, that decision would have been more likely to be seen as having national relevance that would make it reviewable by the supreme court. Instead, it's merely addressing the very specific set of circumstances that occurred in California. I'll try to find the piece I read earlier, and post a link.
Edit: Couldn't find the exact piece, but here's one that makes a similar point from CNN:
http://news.blogs.cnn.com/2012/02/07...tes/?hpt=hp_t2