well, think of it this way, what is the main purpose of your audio system?
you want to make it sound like youre actually at a concert listening to it live
well, if youve been to a concert, you know that the speakers are in front of you, the BAND is in front of you
also, do to the different wavelengths of the speakers to your ears, it will degrade your sound quality
some people say...well if its better, then why do all car companies put 4 or more speakers in cars?
well, the answer is simple--99% of the people you talk to do not know anything about audio--and if their car starts coming without rear speakers...people will feel like the car company is just trying to skimp out on another cost...
most people will think "the more the better"--when in fact its the exact opposite....if i could have a single speaker that produced every frequency accurately--id be all for it