Pardon my ignorance, but can anyone explain how fuel is paid for for this kind of flying in the UK? In my PPL days in the US you paid for the aircraft by the hour and the owner reimbursed you for fuel purchased at distant airports. But this guy's behaviour seems more like someone trying to save money by putting in the minimum possible fuel. Otherwise why didn't he do as has been suggested a couple of times earlier, put in the amount he'd calculated he needed, and so expect to return it with the same fuel load as when he collected it (which was by definition acceptable to the operator).
I must say that (based on obviously limited information) it seems like the guy got off because he had the money for a first class brief and the contacts for impressive expert witnesses.
One indirect benefit of the prosecution, though, has been to make every GA pilot who reads about it think a bit more about fuel calculations - not for fear of prosecution, just because they've been reminded what can go wrong.