Genghis:
I believe the aim of the air test was mainly to prove that the performance was still meeting the FM posted performance.
Off the top of my head, I can only think of one accident where the aircraft didn't meet the performance published (and this appeared to be a generic, as opposed to airframe serial number specific problem).
And I suppose the authorities are going to say that Safety Management Systems will take care of this as well.
It would be nice to see something like this written in to the ops regulations somewhere so that we could be sure that the aircraft were meeting the certification requirements they were originally approved under, but I'm not overly worried if the annual air test is not something the authorities have to approve on an annual basis.