Umm. My HDMI cable is about 6yrs old, but its embedded into the wall. As all the cables were burred into the wall and plastered over. However it was a very high quality cable that cost me best part of £80 at the time.
HP, Dell, IBM/Lenovo Certified Server Hardware engineer.
I had this issue with a Freeview setup when we bought a replacement PVR and connected it to the TV with an HDMI cable. I was able to cure it and get a clean picture by playing with the positioning of the HDMI cable ensuring it wasn't running too close to the other cables (aerial, power, etc) behind the TV.
Sorry, i do not agree with your fault finding thought process.
The picture quality was fine for the past 2years, and up to yesterday when the V6 box was installed.
Technology is also moving on. I have had to throw out a couple of leads that worked fine with older equipment but then show up issues with new. I would also steer clear of the cheapest leads, as the cheap ones on the market are poorly screened & basically sub-standard.
Cable customer since 1993. Services: FH TV, Sky Sports/Cinema (2xV6), Talk Anytime Phone, 350M BB, Virgin PAYG Mobile