People tend to forget that the truth of one thing doesn't make the truth of the other. Take this sentence:
"The average man is taller than the average woman"
If I grab a man of average height and the two of us start walking the streets of any major city, in less than 5 minutes we'll find at least half a dozen women who are taller than he is. Does this make the sentence above stop being true? No, it doesn't. The same applies to dick size.
Also, I'm sure most of us would agree that the larger a guy's dick is, the less concerned he's going to be about anyone seeing it. Therefore the average size of "dicks on display" will be larger than that of the population. Hence guys doing comparisons will draw incorrect conclusions because they're working with skewed data.
--------------
To jump tracks for a second, if you grab a bunch of guys who are 'showers' and compare them to a bunch of guys who are 'growers', the 'showers' will have an average soft size a good bit larger than the 'growers', right? That's why they're called 'showers'.
I do recall reading in college that a statistically significantly higher percentage of men identifying as African American are 'showers' compared to men identifying as European-American. Assuming that information is correct, it makes sense that the average African American dick is perceived an larger than the average European. And this is ON TOP OF the already skewed data.
Lastly, how does ANY of this have any connection with how much fun you have in bed with a guy?