why do people feel the need to buy expensive cable

Taters,
I agree that some people buy expensive cables for various reasons that you mentioned and I know for a fact there are some that have an unlimited supply of funds and think that more expensive must equate to better sound.
On the other hand there are those such as myself that have a limit on what can be spent and in the past I have demoed a variety of cables of all price ranges and let my ears and pocket book tell me what sound I like and what I can afford.
I guess the bottom line is one can’t classify all into one category.

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.

There are certainly some people who buy expensive cable for the reasons you state, but others who can actually hear what they're buying and are confident in their ability to assess the benefits the cable brings to the system and that the cost is appropriate for that level of upgrade. When I had my big Naim system, the benefit of the $1000 HiLine IC over the one supplied with my CD player was a very significant upgrade and much less expensive than upgrading my amplifier or CD player at the time. It's all about what you can actually hear yourself. Don't assume others can't because you can't. Some say they hear the difference between the two sides of the Linn felt mat. I don't, but I don't presume they're deluding themselves just because I don't hear it.

Why not i buy what sounds best.

Do you really believe that the cables make little or no difference? Would you consider a Radio Shacke receiver and bookshelf speakers with their factory supplied cables able to match an all MBL system with Cardas Clears? The system is only as good as its weakest link. I do studio mastering. The difference in detail and accuracy between cheap cables and reasonably priced high end cables is not subtle. It's true that the improvements shrink as the prices rise but isn't that true in every field. Is a Porsche 911 really five times better than its cousin the VW Beatle? Is the Porsche 918 really 10 times better than the 911? Is the the Bugatti Veyron three times better than the 918? The answer is an emphatic "no" if all you could afford was the Beatle in the first place.

One should to match the qualities if ones system with the quality of the cables to be owed. If you don't you will only be strangling the reasons you bought the equipment in the first place.

Don't buy Audioquest Wild Blue XLR interconnects to connect a $500 preamp to a $600 power amp. Match it to something like the Red Rivers. That way your system will be balanced in terms or performance and sonic quality and you won't have to worry about the rest.