Mick,
Your comment is something that I've long suspected. Briefly, it's the client's imagination that really is at work here. Consider these examples.
Sporting good store employees say that diverse color/shape fishing lures don't really catch more/bigger fish. They really catch fisherman, however.
There is a story about A.J. Foyt and some of the mental games he used to play on his fellow racers. Goodyear made a racing tire which was delivered with a red-dot painted on the sidewall. A.J. quickly painted over these dots with blue paint. Because of his skill, he ran faster laps. Goodyear then started to receive several angry calls from racing teams complaining that A.J. got preferential treatment with a superior tire compound.
Like anything else, I guess it's the man, not the metal.