Oh, an average person can tell the difference between those. I'd say an average person can't tell the difference between a system that costs above 3K. The problem is that a lot of people assume that louder sounds better on some instinctive level, and crank up the volume enough that it overpowers on the ears. That's the problem with telling the difference between the systems.

That being said, I have a $500 system that's OK. The fidelity is good, but I find the surround's low mid lacking and the projection is a bit limited, so you really have to make sure the speakers are in the right spot.