To amend my previous post (which so far hasn't been answered):
I have no hesitation believing, that if there's a real "program" at Sky, that they don't worry about the controls - whether their stuff is undetectable or they are protected, both options would be highly plausible.
But USPS wasn't taken down by the testers, and neither was Festina or Fuentes. What got them were police investigations and witness testimony. And I don't see what protects Sky from either.
Thom Weisel probably didn't and doesn't give a **** about being associated with doping, beyond what it costs him financially, and the only thing Bruyneel cares about is being allowed to continue working in cycling. But I don't think the same goes for Brailsford or even Wiggins (for Froome the risk would probably be worth it).
Call me naive if you want, but I don't think the people at Sky would be willing to put all that on the line just for a trophy.