What is the purpose of

Hi. I am fairly new to Audiogon and if this question has been discussed before, I apologize. Reading this you will realize I know practically nothing about electronics, and even less about component design. When you look inside a piece of equipment, you usually see very thin wires used, to say nothing about the fuses commonly seen, with a wire about the width of a hair. Then, when the signal finally reaches the speakers, there is usually more very thin wire throughout the crossover. So what is the point of buying (sometimes) obscenely expensive interconnects and speaker cable? Isn't the audio signal chain only as strong as its weakest link? Or am I missing something obvious? Any answers or comments would be greatly appreciated. Thanks.