"Registered voters" doesn't mean anything. Half of these people won't vote. "Likely voters" is what you look for.
And if so many people are in favor of gαy marriage in CA, why did CA voters reject it when it went up for state wide vote? Why did the 9th circuit declare the ban unconstitutional, if they had any faith that the CA people would simply vote it in later?
I suspect liberal BS in this poll to put pressure on the Supreme Court not to overturn the 9th Circuit ruling. I think it's very likely propaganda.