1) Nobody anywhere has ever said Wiggins had that amount of body fat. He's claimed the 4% figure in the past, and this is easily verifiable using google (he posted it on the guardian website, in an article he authored himself, in 2007) - he has since lost weight from that point and the Sky website lists him as 69kg. Now, how does a man, with a mediocre record at best 5 years ago on the road, and with 4% body fat at that point, LOSE weight and become one of the best time trialists and climbers in the world? Seriously, there's no medical explanation for it unless he was lying about his numbers.
2) Everyone claiming Cancellara wasn't fully fit conveniently overlooks the fact that he won the prologue by a reasonable margin. Can't have your cake and eat it too.
3) It's not quite as simple as setting a pace and then the racing having natural attrition. We've seen circumstances where Sky had 40% of the riders in the lead group. That's not natural attrition and riding tempo - that's setting a pace which is absolutely blistering and only the best being able to stay on.