It's possible to distinguish natural diamonds from synthetic diamonds because diamonds can't be melted down and recast, so the impurities and flaws of natural diamonds set them apart.

Gold, on the other hand, is routinely melted down and recast.

> People seem to want 'the real thing'.

Correction; women seem to want 'the real thing', but diamonds aren't themselves valuable, they are a status symbol. Girls don't want to show their friends a "fake" diamond and unfortunately due to marketing, they consider man-made fake even though it's real.

Somehow I can't imagine lab-produced gold being worth less than naturally occurring gold for jewelry, etc. I imagine the only potential difference would be the distribution of isotopes. But I suppose it could still happen if large players would benefit.