i think those that are claiming engine failure as a crash are also unsuspecting gas engine users who have not given thought to a faulty spark plug coming into the equation either.
it's usually when something fails that has been a piece of hardware known for this that the user becomes more involved with their gear and then find out from others that the plugs are known to poop out at inopportune times. reallistically speaking though, if these plugs are failing, then why are they supplied with the engines?

when APC started making props back in the early 90's, Dad and i were given sample props to test for performance on our competition Free Flight planes. my prop threw a blade, thus blowing half the model into pieces from the vibrations that ensued.............Dad took his prop off and reinstalled the tried and true FG props we always used. we were later told hmmmm, i guess the props need to be beefed up in the hub to withstand the aggressive HP the OPS 45's were putting out at 23,000rpm...........so was it my fault that a defective piece of hardware destroyed my plane, or was it the test prop from APC?....especially since we were told that these props were designed specifically for FF comp engines.

i will study every aspect of any piece of hardware used in a model i build and fly so as not to have silly mishaps, but there are plenty of people in this hobby who simply buy what's on the shelf, install it, then go out to have fun as it is intended.................bottom line, the plugs should not be supplied with the engine if it is not of the same quality or better than what they are being replaced with, so YES, it is the mfg's fault when an unsuspecting flyer crashes due to a part that the mfg supplied.