Did you do it blind? Did you give it the Pepsi Challenge? Expensive cables are marketed directly to idiots. Just because a difference can be measured with a meter, it doesn't mean the difference can be noticed by a human. There's a big reason that the markup on any computer or a/v cable is through the roof.
As I recall it was a blind A/B done in our office showroom. Every part of the system has a hand in the final output, I'll use audio because that's what I'm more familiar with, also being somewhat colorblind makes it harder for me to evaluate video.
If you take a 2 channel stereo system and swap out the source, say a CD player, or turntable you will get a different sound, swap out the receiver or amplifier and you will also get a different sound just like changing the speakers all the individual components add up to an end result. The signal going from stage to stage in the system has to get there along interconnects and other cabling, the signal is subject to all kinds of things that can distort or impede the original signal. If that signal get's altered the end result is going to be different, it is after all the sound, music, etc. that you want to hear that's come off the original source. A good cable is going to make help make sure that the original information get's there w/ as little interference and in the right order.
Now it's all relative, are you going to hear a difference listening to music through the crappy speakers on a TV? No, probably not, there's also a point of diminishing returns where the amount of bang you get for your buck will be less and less. To use the original example, I doubt any TV you can get at Bestbuy is going to really be worth spending that kind of money on a HDMI cable. Nor would I ever probably spend that kind of money on a cable, I don't have the means to afford the type of system that would actually make it worthwhile, but if you have a decent system, then yes cabling can make a difference, absolutely.
