If you walk into any electronics department you'll find a ton of different cable options for TVs and stereos. Chances are you'll also find a salesperson trying to convince you to buy the most expensive option. When it comes to digital cables, though, all of them are essentially the same.
Cheap HDMI cables give you the same results as expensive options. CNET's results were the exact same, and Digital Foundary echoed the statement as well. The fact is, you won't see a difference between cables that transfer digital data, like HDMI or DVI. In fact, our friends at the Wire cutter recommend the $10 Monoprice HDMI cables, which is about as cheap as it gets!
Analog audio cables are the exception, and likely the main cause of this myth. Analog cables will cause a change in the quality of sound, but unless you're a hardcore audiophile obsessing over every aspect of sound quality, CNET and Gizmodo both agree that most people won't notice the difference (unless they're really paying attention). So yes, premium speaker and audio cables technically make a difference in the sound quality on high end stereo equipment, but most of us will never hear it.
Common sense also applies here. If you're running an iPod with crappy MP3s through a $500 stereo, spending more than a few dollars on speaker wire or audio cables isn't going to do anything for the sound quality. For most of us, the cheapest cables off the shelf (or off the internet, as the case may be) work just as well as anything else.
See tomorrow for next myth!!