Two things:
“The digital content in the HDMI cable does not change between your video player and TV any more than your photos do going from your digital camera to your hard drive”
...which is to say what, very little, though ocassionally quite drastically? I know I can't be the only person who's copied digital photos from the camerea o PC (or from one drive to another) only to find some sort of writing error has rendered half the picture missing, or its color spectrum inverted. Probably happens 2 or 3 times out of 50, but still...
and:
If you want to see how good (sic) your HDMI cable is, connect a true 1080P HD source to a display via HDMI, make sure you're getting a true full 1080P image, and then start to move the cable. Bend the jacket the way that cable might get bent if it were routed around the shelves of your A/V cabinet or (gasp!) through the walls of your home. And watch whether the display loses sync or drops to a lower resolution. I'm not talking about jiggling the actual connectors (though that too will often have deleterious effects), I just mean bending the cable. Lots of HDMI cables are made to such poor tolerances that simply changing the distance between one of the conductors and the insulation will have a demonstrable impact on performance.