I asked for an opinion from a decent pianist that I know on why are steinways so expensive, albeit quite a while ago, and he never commented on sound. The main comment was getting the balance between a good action to play on, and one that lasted with significant use. Pianos do wear out with use. Old pianos generally should be considered like an old car.
One thing for certain is, marketing certainly plays a major role. Having big names use or endorse the gear certainly sells units. Certainly in the case of beats headphones and monster cables, that's completely marketing, while the cables are overkill, the headphones suck.
When it comes to luxury items, the french seem to have it mastered, particularly with alcohol, where their drinking end price range isn't particularly good at all (I'm Australian, local wine becomes quite drinkable if you spend >$20 a bottle), then their cognac or champagne, it's all marketing by having a it named after a region and protecting it so viciously.