Okay, I'm sure I'll be called anal for this correction ... Frankly, I'm okay with that ...
True, bass frequencies are not directional. However, the frequencies that give the bass it's tone and character certainly ARE directional. So while the lower frequencies will appear to come from everywhere, the upper frequencies will not.
Another thing ... Let's talk playback ... Bass frequencies also take the most power from an amplifier, because of the large movements required of the speaker. panning the bass to any extent left or right will have one channel of your amp working much harder than the other.
It's just a fact that the bass is generally close to centered for most recordings in most genres. It's not that way by accident. That's really just where it works.
I'm glad to see someone mentioning 'good monitors' ... If you don't own decent monitor (and I do mean MONITORS, not nice -- or even REALLY nice -- home stereo speakers), it's hard to understand what you're missing. Once you have a good pair, you realize you CAN'T LIVE WITHOUT THEM!!
We love you all.