One of my American friends was surprised to hear that British kids trick or treat on the nights leading up to Halloween. I think this stretching of the feast is to do with the conflation of Halloween and Bonfire Night. In the olden days- which aren't actually so long ago- when Bonfire Night still mattered, kids used to trek round the streets in the weeks before November 5, carting an effigy of poor old Guy Fawkes, demanding "A Penny for the Guy". Now they trick or treat instead, but because it was valid to treat Bonfire Night as a season they do the same with Halloween.
Meanwhile, Guy Fawkes has mutated- thanks to V for Vendetta- from a scruffy old Jacobean with straw coming our of his sleeves into an ultra-cool symbol of protest and resistance. Look at photos of the Occupy London crowd and you're likely to spot several people wearing the mask from the movie- with the pointy beard and the sinister-cum-jocular grin.