I definitely think there is either a better speaker or some sort of volume tweak. I have two iPhone 4's and one iPhone 4S and the 4S is clearly louder.
In a test it does appear they are stereo. Very cool. I hadn't thought about it either until this string enlightened me there were two speakers Thank you!
hmmm, must be something wrong with mine, if I cover the one on the bottom all sound goes away. Nothing plays from the top center speaker...at least not with music from itunes...
Also take a look at the user manual which is bookmarked in Safari. Go to the link iPhone at a glance and then iPhone overview. That's where Apple Care referred me when asking about the hardware.
They aren't talking about that part, he is talking about the "speaker" under the proximity sensor. Like when you answer the phone and hear someone speaking.