The difference is that Prop 8 was a Constitutional Amendment. I guess they couldn't figure out how to say a Constitutional Amendment is not Constitutional.
I think they wanted to leave the easier process for legalizing homosexual based marriages by petition.
I think they know they screwed up when they did not force the legislative issue prior. However the judges assumed since they legalized it, the people would be sheep. (or allow the sheep to be married)
The 18k IS a poison pill.