I found this kind of strange also. I mean manning isn't what he once was, but Denver's D is still scary good, and we have seen many teams win championships with medicore QB's, and a strong defense.
We did an office pool with 20 people, and you had to lay our the bracket before the wildcard games started. Not one person picked Denver to go to the SB! I was avoiding them as I assumed many would pick them, and wanted to have a chance to win it all and not split, but I didn't realize how much people thought they were going no where. Was very curious.