The power cables put out electro-magnetic interference that can affect the signal, causing noise in the audio and distorted images on the video. EMI is something that is ut out by every electrical cable whether it's long or short, AC or DC, a few milliamps or hundreds of amps. It's still there to some degree.
I'm don't going to argue your experience or skills, but the general consensus is that power cables and signal cables should be seperated. That' not just by this crowd, but also by the high-end car audio crowd.