As I recall, the UK also surveys aircraft movements, the concern being that this gives the impression that hours are declining but fails to take into consideration the move towards flying from farmstrips (i.e. may understimate flying). There's another document out there (near the top of the search list) that gives more details about how the accidents were counted.
The UK and USA figures were originally posted more to argue that they were within the same ballpark, which is to say that general aviation remains an order of magnitude (or so) more dangerous than driving in a car in both countries. To really argue against this, you'd have to argue that the aviation statistics were out by an order of magnitude, or that the driving statistics were considerably different in both countries - which of course they are. Obviously arguing that they may be out by a factor of 2 or 3 weakens the argument somewhat, but there's still considerable latitude for being wrong, and still being right.
I agree that the US publishes very good statistics, but part of the reason for this has got to be simply that there aren't enough aircraft or accidents to make this worthwhile in most other countries. The UK statistic was calculated from data collected over the course of a decade, and still only covered about 140 accidents. This makes for a 95% confidence interval of about 120 to 170, without even taking into account the fact that we're not sure how many hours were flown not to mention all the other (valid) concerns about fleet composition etc.