It has already been said but I will corroborate that factory Harley exhaust is actually very quiet. It may have changed but when I bought my bike new in 2001 and ran the factory exhaust it was quieter than 99% of performance vehicles on the road (sports cars, sport bikes, other motorcycles, etc).
Now I have changed from the factory exhaust to one that is louder than stock but after installing it I also went out and purchased the "quiet" baffles to tone it down some.
I also LoL'd at the headphones linked to engine rpm comment :) Reminds me of this article:
http://www.caranddriver.com/features/faking-it-engine-sound-enhancement-explained-tech-dept about sports car manufactures piping "performance" sounds into the cabin of cars.
Oh and as a Harley rider I also agree that "loud pipes save lives" is bullshit. If you are overtaking at a slow enough speed to be heard then you would be able to safely navigate away from danger. Typically, if you are overtaking much more than 5+ mph faster you will be abreast of someone before they ever hear you.
