Yep, devices do vary in their ability to drive the cable.
I've got 2 identical cheapo 5m cables feeding the TV.
The Set Top Box link is 100% OK. Never get any issues with that.
The feed from the blue-ray player can be hit and miss. Occasionally, I hear a thermostat go over and it causes a glitch in the video and audio, so, clearly the blue ray is a bit marginal at driving the cable. That said, I think it might be set up to upscale everything to 1080p, whereas the STB only outputs 720p, so the bit rate will be much higher.
So, yes, cable length and definition of content combine to challenge the cable. SD over a short distance, any bit of wet string will be fine. HD over longer distances and you might need to find a better quality cable.
.. and you don't always get what you pay for, so expensive doesn't necessarily mean quality!