Why the Chiefs won't go undefeated:
1) History: no one has ever gone 16-0 in the regular season before

2) A bad team heading south could certainly salvage some pride if they were able to knock a powerhouse team from the ranks of the unbeaten. I could easily see the Raiders ignoring an opponent or two in order to gameplan against the Chiefs.

3) They are giving up too much yardage, and have won only because of big plays at just the right time....

Why the Chiefs will go undeafeted:
1) The league has only been playing a 16-game season for 25 years. That's not enough to say they can't.

2) The Chiefs will not be looking past anyone on their schedule. Additionally, they have not shown any tendency to play flat enough to lose to anyone. If they were going to lose to anyone, they would have lost to a balanced and lucky team like the Broncos, or to one of the best defenses playing at home like the Ravens, or to a team playing at home with a 17-point lead and a legendary mystique, like Brett Favre and the Packers, or in a grudge match against a team struggling for pride on its home team like the Raiders. But they won all those games.

3) People say that KC won some of their games with smoke and mirrors, but I'd like to point out that the big plays were certainly by design, not chance. Kansas City emphasizes special teams and takeaways on defense more than most teams, and it has paid off. Furthermore, just because Dante Hall scored a TD return, it doesn't mean that KC couldn't have easily scored with their offense anyway. In each of those cases, KC had plenty of time to drive down the field with their numerous offensive weapons....as evidenced by the quick scores in Green Bay when they had to.
Look, KC has been getting quick scores for a full season and a half now. They proved last year that they can score on anybody when they have to. But they don't always score easily early in the game because it isn't desparate. Against Baltimore and Oakland, they played patiently, trying things out, going for the home run perhaps once too often...but then, that tells you things about how their defense reacts. You really have to consider that the 3-yard run by Priest Holmes in the 2nd quarter that puts them in 3rd and long (after which Tony Gonzalez or Eddie Kennison drop a sure 1st down) gives them the information they need to hit for a 50-yard strike late in the 4th.
The difference this year is that when KC scores quickly (or goes 3 and out quickly...it always seems to be one or the other), it leaves the defense on the field for a longer time. But this year they aren't giving up the points. Whenever the opposing team gets down in the red zone with the game on the line, the defense has tightened up and gotten the stop.
And even that isn't just luck. The red zone is different than the rest of the field, simply because of space. Opposing teams have noticed that our defense is speedy but light. So they spread us, create some space, and try to make us miss the first tackle. That's how they get the yardage. But in a confined space like the red zone, the speed makes a difference in getting to the quarterback or stepping in front of the ball for an INT. Which is what has been happening.

KC is for real. There are good and valid reasons why they probably won't go 16-0. Both Denver and Minnesota remain strong tests, and if the lower-tier teams make their game with KC their superbowl, KC could face 8 tough games in the 2nd half. But they are rested, skilled, and they won't ever give up, because they've gained confidence from some of the close games.

Maybe this is the year the record falls...?