As an ex-RAF groundcrew member with a life-long interest in aircraft, I guess there are a multitude of inter-linking causes-and-effects here.
The almost saturation servicing with a large manpower resource in a service environment; availability of relevant spares and POL (no visible cost); constant aircrew training and perhaps more in-depth introduction to type; possibly stretching the boundaries of normal usage of the a/c by air-show performances rather than standard in-service flight envelope.
I recall an accident a couple of years back when one of the 'Vintage Pair' fell down. One comment from a gentleman who used to fly the type was that a certain manouevre early on take-off had probably caused the problem. This was flagged in the service pilots notes, as hard experience had shown it up. Said experience has to be re-learned if the pilots notes are unavailable to the aircraft renovators and current operators.
It would be interesting to compare the accident rate for 'preserved aircraft' (lack of a better term) in UK with that in Canade/USA where the numbers are so much larger but the governing attitude seems to be more relaxed.
None of this is to decry the guys who perform wonders every year bringing historic aircraft to us punters, whether at Old Warden or Fairford. It's just that warnings like 'Careful, she bites', posted by the original operators, can get lost over time.
Long may all the pilots and ground crew flourish, though. Museums are interesting to a point, then you need the sight, sound and smell of the real thing (or very close approximation)flying.
Regards
RonBVR