I believe Google actually did some research that concluded something to this effect, and it was a big part of why they started pushing Go internally. Whether or not that's the right conclusion based on that data is debatable... I'd argue not.
Why not? It seems reasonable to me that as the number of people working on some piece of code grows the average skill will settle around "not an expert", whatever that means.
I'd tend to expect the same (and agree that "not an expert" is vague), but I'm actually a bit more curious about the proposal that it's a normal distribution. Why would it be? If I had to guess, I might go for something downward-skewed, or maybe even some kind of typically bimodal thing.
