I havent been cycling for long, so my opinion isn't worth much, but i've always discounted the average speed statistic. Unless you are on a track, it seems dangerous. Especially for people who ride on the streets, and on trails that are shared with pedestrians. Not only that, but it seems like its something that could suck the fun and beauty out of the experience.
I dont want to be tempted to run red lights. Be too impatient to stop to take a picture. Or not want to slow down when I am passing by a family.
I suppose its different for pros or cyclists aspiring to be pro's. I'm just cautious of burning myself out on this great hobby of mine.