Here is the other side of that
If R&T is correct that engine failure is not a result of engine oil breakdown rather it is primarily caused by poor cold engine driving habits, then the 10% or 5% engine failure which could occur prematurely can be avoided by following their recommendation by driving conservatively until the engine is at operating temperature, so there is no need for the extended warranty, at least so far as engine failure is concerned. There are many other parts of the car which can go bad prematurely and make the warranty worthwhile, but engine failure may not be a justification for spending the money. The extended warranty for my car is around $2000, and if we put the engine aside, what is the likelihood of incurring $2000 in expenses for other items needing repair? I don't know the answer to the question but I don't believe it is obvious.