Originally Posted by oldskewel

I don't know why they do what they do. But I do know ...

If the torque procedure does actually cause plastic deformation ("yield"), then that procedure (e.g., removal and reinstallation) cannot be performed indefinitely. Each time you'd re-install with a little more plastic deformation, you'd be moving closer and closer to the ultimate tensile stress ==> fracture.

So if re-using, and yield may have occurred previously, you can't blindly do the torque + angle installation procedure. You need to be a little smarter and more careful. Knowing that might be beyond the ability of many professionals and DIYers, that could be why BMW decided it's pretty easy to just say re-use them.

BTW, other stuff that might be safety related, and is easy for BMW to say (from the owner's manual):

"For your own safety, use genuine parts and accessories approved by BMW."

"Installation and operation of non-BMW approved accessories such as alarms, radios, amplifiers, radar detectors, wheels, suspension components, brake dust shields, telephones (including operation of any portable cellular phone from within the vehicle without using an externally mounted antenna) or transceiver equipment (for instance, CBs, walkie-talkie, ham radio or similar accessories) may cause extensive damage to the vehicle, compromise its safety, interfere with the vehicle's electrical system or affect the validity of the BMW Limited Warranty. See your BMW center for additional information."

"For your own safety: use only brake pads that BMW has released for your particular vehicle model. BMW cannot evaluate nonapproved brake pads to determine if they are suited for use, and therefore cannot ensure the operating safety of the vehicle if they are installed."

Similar thing on BMW-only wheels.

Snow chains only on the 17" wheels.

"In order to ensure the safety and reliability of the brake system, have the brake fluid changed every two years by a BMW center"

I'm sure that's all fair advice, and for some people, they'd be better off following blindly rather than thinking. But it also shows that BMW will say things in the name of safety that may be overly conservative for people who know a thing or two.