You have to see what a system can do first and that's down to the details. Placement, the room, speaker stands, cabling, power. All these things can sometimes make a system sound ten times better than it did because they were overlooked.
why do people feel the need to buy expensive cable
I have tried expensive cables and one's moderately priced. I would say there were some differences but I can't actually say the expensive cables were better. IMHO I believe a lot of people buy expensive cables because they don't actual trust their ears and are afraid of making a mistake. They figure the expensive cables are better for the fact they cost more. If you have a difference of opinion or share the same thoughts, I would like to hear about it.