Even STREETLIGHTS, in todays society have "Halloween 2010!" or "Halloween Horror Nights" and stuff. It would of been creative to have some of that up.
I am sure that some decorations such as cobwebs, and plastic tombs would have been obliterated, but garden gnomes, boxes of cereal, etc.. survived so, so could a Halloween Banner, costume, lantern, etc.. could survive. I just want to know why Bethesda didn't get creative with Halloween stuff when they got ownership of the game. It was Halloween when the world ended, and when the world ends I doubt people bother with taking down left over decor.