Not all cables are the same, even in the digital domain. Cheap metals, shielding, high resistance wire and stray capacitance can change the shape of the signal

Not all cables are the same, even in the digital domain. Cheap metals, shielding, high resistance wire and stray capacitance can change the shape of the signal, increase noise and increase losses. What goes in doesn't always come out the same and cheap shitty poorly filtered equipment on each end makes it worse (PS3, Vaios, low-end Bravias etc - yes I'm complaining about Sony here). However the problems go away immediately at the $10 price point. I'd only buy an expensive cable if I was going to require extra mechanical strength i.e. if it was being plugged and unplugged regularly, much as you should always buy decent oscilloscope probes. On a side-note, as an ex-EE I've seen some crazy shit going on with cables before. The worst being a $1500 RF cable that ran 4 inches between two bits of avionic equipment and carried 455KHz IF (nothing particularly sensitive or reliable that a $15 cable would have sufficed).