alwatson:
One thing that I find interesting is that as somebody who sells TV equipment and related accessories (in a national chain many of you wouldn't consider going in, but anyway...!) I have asked my superiors that if the expensive HDMI cables we are supposed to sell make a difference to picture or sound, why don't we have a simple demo in store which shows the difference?
The premium HDMI cables we make lots of money. The margin on them is very high. We would sell lots more if it were possible to demonstrate the benefits in store rather than saying "honestly, if you don't see a difference then bring it back" because many won't spend £50 rather than £5 on a cable when I have no way of showing what difference it makes. We have a demo showing identical TVs connected to the same source with composite, scart, component and HDMI to highlight the difference so I don't think a similar demo using different HDMI cables would impossible to get going.
If you can demonstrate something is better, people will often buy it. An example of this is when people come to me looking for an iPod dock, many people want to spend around £50 or less. In many cases I show them what they could get if they spent a bit more money. Something such as the Logitech PureFi a Sony which cost £90-100. I was initially surprised how many people would happily pay the extra after a demonstration, but I suppose if you know something is better and you can afford it you are fairly likely to buy it.
None of the stores I've wandered in to, and I struggle to walk past an AV store/department without going in (much to my girlfriend's annoyance), have had a demo set up showing the difference between HDMI cables. This includes national chains, department stores, brand specific stores and specialist chains. Maybe the more expensive independant type of store would be happy to set up a demo if somebody asked them to, but I've never asked.
For the record, I'm of the "if it's well built and complies with HDMI standards it will be fine" opinion. I have yet to see any difference between HDMI cables I have used both at work and at home besides the quality of the construction. I think the reason nowhere has such a demo set up is because even less people would buy the expensive cables.