why do people feel the need to buy expensive cable

Because the cables are usually better.  How much better depends on what makes your ears happy and how much you willing to pay

jmcgrogan wrote "This thread makes me wonder if car enthusiasts on automobile websites bash Mercedes and Porsche, because obviously any Ford or Kia will do." 

If you look at the bodies of a Kia and Porsche or under the hoods of a Kia and a Porsche the differences will be obvious to any human with a brain . If you dress two cables of the same gauge and construction with the same fancy jackets and cut them open to look at you will not see the difference . So this luxury car comparison is strange .

What Ford or Kia owner thinks their car is in the same class as a Porsche ? 

I dont have a dog in this fight and I could care less what others use for cables but these empty arguments are ofetn hard to ignore and laughable to say the least. jmcgrogan are you really trying to say that the performance between the two wires you mentioned are as dramatic as those between a kia and a porche? Surely you do not mean to infer this.

 The differences between those two automobiles as well as the boats you cited can easily be distinguished through a series of basic performance tests. Unlike cables this is pretty cut and dry.

However iif we were to measure these cars from a purely subjective standpoint such as asthetics or pride of ownership....well now we are wading into murky water...you know like cables.