I'm going to say that based on my observations, this is absolutely, 100% true. I live in the tropics and it is very easy to observe with non stainless steels like m4. Actually, I cleaned fish yesterday morning with my m4 Phil Wilson and afterwards I rinsed it briefly and sharpened it to an edge that would instantly bite when touched to my beard. Last night I went to put it away and it had completely lost that level of bite. Now that is an extreme example and was likely due to me not fully cleaning all the fish blood off or not completely drying the edge, but you get the idea. The edge of the knife is more prone to corrosion than any other part of the blade. Depends on a lot of conditions but it is a very real phenomenon.