I read that, it is a common belief that I don't follow.
The plug chart is a good pic and explanation of what plugs should look like. Some of the why the specs are there because of fuel ect... well make your own conclusions.
Here is another one that we teach at the EFI101 class that is adopted by everyone that I don't believe either.
"More fuel supresses detonation."
I have read that posted here by a few people and I believe it not to be true either. We have proven this on the chassis dyno again and again but it is a common belief out there that everyone follows. "If it is detonating then back the timing down and add some fuel." I agree back the timing but the fuel does not stop detonation.