The way it was always explained to me when I was starting out is that many things you hear in the world are really not stereo sound. For example somebody speaking to you like in dialogue, interviews etc is only emanating from one point. While the fact that your ears interpret it in a stereo fashion it does not make it stereo.
Now for something like a band where the drummer could be positioned 20 feet or more from various other instruments it does make a difference in our perception of the sound environment. The reason I mention this is that during playback you have the same issue. If you record something in stereo but play it back on an old tv where the speakers are 3 inches apart is it really stereo? Now if you play it back in a home theater set up for surround sound you will defiantly hear it.