> The difference between an iPhone with the default earbuds and a $5000 stereo rig with speakers is astounding but only a tiny fraction of the listening public cares

Without optimum room design, even half-decent earbuds are better than pretty high-quality speaker systems, if you don't need multiple simultaneously listeners.

And I don't think it's that most people don't care, I think it's just that most people have a utility function where the additional utility of high-quality sound gear is far too low to ever be justified by the cost of the gear (and the necessary environmental improvements to make sure that the effect of the gear isn't wasted.)