Simon I do not think that the issues that you raise are in any way peculiar to Canon.
Every manufacturer will have a percentage of failures (including Nikon).
Anecdotally, I shoot with Canon equipment, and while I do try as best possible to take good care of my equipment, in rather harsh outdoor conditions in Australia, and elsewhere, the bottom line is that my equipment takes a hammering.
Nonetheless I have never had any (camera or lens) equipment failure.
Tripods, bags, and other stuff have broke.
I once dropped my 500mm f4.0 three feet onto my foot. How I did not break a bone I don't know.
The lens was fine - just needed a dusting off.
I shoot in hail, thunderstorms, and rain, so that many people regard me as completely barking, with a 40D, 5DII, 5DIII, none of which are fully weather sealed. The Canon reps go pale when I recount this but the cameras and lenses soldier on with no problems.
I have no doubt that at some point I will buy a dud (and that Canon will honour the guarantee and replace it) but the stuff that I have is worked really hard with no problems.
If you want to change to Nikon, you mentioned the D800, do it for the perceived benefits of good image-making not because of concerns about reliability. Ultimately given the scale of production I don't believe that there are many differences in tolerances and quality assurance between the major manufacturers.