The singe biggest factor to consider in why Prop 8 passed was the Obama effect. Due to Obama high numbers of African American and Mexican voters who traditionally don't vote voted... and as Prop 8 was the same day they voted on that as well... and voted for it by a huge majority. Without Obama running for President Prop 8 wouldn't have passed and as long as any vote to repeal it doesn't fall on the same day as the Presidential Election it should e successful.
This is a brutal piece of misinformation. CNN polled exactly three areas in Los Angeles before coming up with that story; when you look at the margin of Prop 8's passage and compare it to the number of African-Americans in California, it becomes clear that even if African-Americans voted disproportionately against Prop 8, they couldn't have affected the vote to that degree.
Running a Prop 8 repeal in an off-year election would be a bad idea because the off-year elections (like the one coming up in November) attract only the 'hard-core' voters; most of those are old white people. Seriously, Prop 8 is a lot like Prop 167, the one that attacked Hispanic immigrants - it's a last gasp from the old guard before they're swept away. And just like 167 tilted the Hispanic population of CA against the GOP, Prop 8 will tilt many young people away from the GOP. We just need to wait a couple of years before the demographic shifts make it inevitable.
When casting blame for Prop 8, by the way, we ought also to take a good hard look at activism within the GLBT community and its straight allies. Gavin Newsom's declaration that gay marriage is coming "Whether you like it or not," was a classic example of shooting yourself in the foot; you'd never see rhetoric that divisive coming out of MLK's mouth, and it gave the anti-equality brigade a lot of ammunition for scary commercials. Then there was that teacher in San Francisco whose coworkers took her 5th grade class on a surprise field trip to her lesbian wedding - while it must have been a very sweet moment for her to step outside with her bride and find all those children cheering and throwing rice in celebration, the footage played right into the hands of the lunatics declaring that the children have to be protected from the queers who are going to seduce them.
Finally, the anti-8 coalition was sclerotic at best - I saw practically no advertisements against 8, and very little in the way of door-to-door canvassing or demonstrating; one of the largest pro-8 rallies in the state was held near my house, and only four people showed up to oppose it. Frankly, we took victory for granted and got sucker-punched for it - and I'm including myself in that statement, because I could have done much more to fight Prop 8 but felt it was guaranteed to fail. I did convince one Republican to vote against it, but he forgot to register to vote. :(
The funny part is, because the Constitution bans ex post facto laws, Prop 8 couldn't do anything to annul the 20,000 gay marriages that occurred between the Supreme Court's decision and the passage of Prop 8, meaning that 40,000 gay people are married right now in CA (including George Takei!) and the fundamentalists can't do anything about it. The mere existence of those marriages works every day to erase the legitimacy of the anti-equality position.