Actually, it is absolutely true that leaving speaker cables on the floor detracts sound quality, but it has nothing to do with electromagnetic disturbance. It is all because of gravity. This has been thoroughly explained by professor Vytautas Kusetus in his ground breaking scientific whitepaper "The Selfish Electron".
Shortly: As everyone knows, besides energy, electrons also have mass. When an amplifier sends an electron to its journey towards the speaker, the electron first has to travel some distance horizontally, but on the last leg of its travel it has to go uphill from the floor to a speaker terminal, and continue even higher to the actual driver. It has to spend some of its energy to defy gravity that tries to pull it downwards, so consequently it has less energy remaining to move the driver cone. This means slower transient response and weaker bass.
Knowing my interest in audiophilia, Professor Kusetus has contacted me with a proposal to start a joint venture to develop a new kind of HiFi equipment rack that enables mounting on ceiling. That way the speaker cables will be mostly vertical and the electrons will travel downhill - this time aided by the gravity! We have estimated that 2 meters of height advantage corresponds to almost 10 extra watts in an amplifier.