I wonder how many of those overclocked systems belong to people who are 100% convinced their system is stable and the programmers of Microsoft and <whatever other applications they're using> are idiots for having stupid crashing bugs.
My system can prime95 for 5 minutes, obviously it's rock solid.
Alternatively, how much of the stats were the same machines failing repeatedly until they found stable settings?
[Anecdote] If my brief experience is anything to go by, overclocking involves lots of crashes until you get it right. Once it is working I would expect no more failures than a shop-bought PC, but by that point the statistics are already skewed by all those crashes that I don't care about.
There are OS's that are designed to survive a fair amount of HW errors, but I don't think most people that OC would want to pay the speed penalty's for that.
My system can prime95 for 5 minutes, obviously it's rock solid.