I have to agree that the British plug has more intrinsic safety features than any of the much less standardized US plugs. But it is significantly larger which has a number of disadvantages.
I spent some time googling around, looking for data that might indicate that the greater intrinsic safety of the British plug is worth it. It turns out that it would take a fair amount of time to sort out, and it may not be possible. The searches turned up no consistently recorded data, and a surprisingly small amount of data overall. The overall impression I got was that the vast majority of electrical accidents (and definitely the fatal ones) occur in industrial settings. Lightning seems to be the next problem and home accidents are a distant third. This trend seems to be world wide.
One interesting thing was that the data is usually divided into "low voltage" and "high voltage" injuries. Low voltage being anything under 1000 volts so no distinction between US and British distribution systems.
I found nothing that would definitively sort out the contribution of plug design, just some off hand comments which may indicate it is a minor player. Apparently a big part of electrical injuries to children is biting through a power cord, something that is independent of plug design.
So I guess at this point I just have to say cheers, and congratulations on having a better polished safety apple.