I recall clearly the first time I replaced the manufacturer-supplied interconnect with an Audioquest Ruby cable. The difference was obvious. I have tried several mid-line cables, like Tara Labs "Pandora" and Kimber "KCAG." Honestly, I can't discern a sound difference between the two. I mostly listen to headphones, so I would expect to hear it there. I think what you pay for in very expensive cables is the complicated way they are manufactured. If you have the means, go for it. But I don't believe you are getting your money's worth.
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.