i see that it's not a popular idea here. no wonder the car companies haven't offered it as an option.
but if you think about it, the mods that you do to the exhaust only gains you 5, 10, or 15hp, depending on how extensively you mod it. it really makes negligible difference to the acceleration times like 0-60 or 1/4 mile. it's just the louder noise that makes you think that you're significantly faster.
so why go thru the trouble of chopping up your exhaust if you could get convincing, aggressive sounds thru your audio system?