My Dell U2410 has buttons that detect when your finger gets near them (they start lighting up) which is pretty slick. Maybe it's just a bit more expensive / harder to integrate and wasn't considered worth it. Not exactly sure how it works but I think it uses the same physical phenomenon as a theremin. Again it's mostly pointless, but it is pretty slick.

> Maybe it's just a bit more expensive / harder to integrate

And probably patent-protected by Dell and needing licensing cost, instead of coming up with something they could patent themselves.