Turns out the whole thing is an error. CD Projekt's told me the patch is much more reasonable--less than 20MB--but an issue with Steam specifically forced users to basically download the whole game all over again. As far as CD Projekt can tell, it's only a Steam problem right now.
"We’re working with Steam to get the issue sorted by Monday morning," a company spokesperson said.
Darn. Gamers with digital pitchforks fighting over 9GB would've made a more interesting story.