willadvise, to clear up a (very small) point of apparent contention: I don't believe anyone in his right mind would suggest pilots should stick in an offset if being radar vectored. (Your original post >>" The controller is expecting you to fly a particular track and makes judgements based on your predicted track only to find you a mile or so closer to that other aircraft that you were going to slide nicely 5nm past."<< )
Is there anywhere except a terminal area where you allow an aircraft to get within 5NM of other traffic? Even in Europe, where I've had same level cruising traffic quite close, I can't remember seeing any only 5NM away. I don't think anyone is suggesting that we as pilots should build in our own bugger factor over a controller's vectors.
Every time I throw the "automatic embedded offset above 10,000 feet" argument forward the same argument is put forth: "There are airfields above 10,000'". Not too many, particularly if capable of taking jet aircraft, but this apparent problem can be overcome with existing technology. As soon as any current FMC-equipped aircraft enters a STAR (and until it exits a SID), the offsetting facility is not enabled. The same feature would fix the problem for any airfield above 10,000'.
Could someone give me a list of such airfields? Maybe in the Andes or Nepal? I've landed above 10,000' in New Guinea, but it wasn't at an airfield - and it's not an experience I'm in any hurry to repeat. Thin, thin air and a very dramatic demonstration of how TAS is the overriding factor over IAS that far above sea level...