They should expect Denver to win. The Broncos are 4-0 and coming off a win against a team that was favored against them. Their defense is #1 in the NFL through 4 weeks, the QB hasn't thrown an interception yet, and that team is getting it done even though its offensive line hasn't played as well as it should. I, personally, expect that Orton will throw his first pick(s) of the season in this game, and I think New England will win fairly convincingly, but I can see where the Broncos fans are coming from.
We'll know soon enough.