Regarding failure and stock thickness, while I do agree quite strongly about design influencing blade use, I have some very thin blades that can handle even heavy chopping without any problems. I have a Bolo from Tramontina for example which is only 1/8" thick, which has a very wide edge grind, which tapers to 13-15 degrees at the very edge.
The main problem with most blades breaking is a lack of impact toughness which causes them to shatter. You simply can't do this to properly tempered spring or carbon steel. However most manufacturers are using steels that inherently are very brittle, or are simply running the hardness too high, because of the current belief that 60 RC makes a good knife regardless of steel or blade type.
If the Ontario khukuri had a proper heat treat, of good quality 1095, the most that would have happened, on a glancing hit into a knot, would have been a slight edge ripple. You should not be able to induce edge blow outs on such knives. However, Ontario has one of the worst QC that I have ever seen, so it doesn't surprise me that it broke as it did.
-Cliff