I'm not sure I believe that. Pocket watches were worn with waistcoats. I am not sure when the average man stopped wearing a waistcoat, but wristwatches were "mass-market" during and after WW2 (massive economies of scale necessary to equip armies with them), probably around the same time. When was the period of history, pre-wristwatch, when men who could afford watches didn't wear waistcoats?

That's what I use them for. I carry a pocket watch, and wear Levis 501 jeans almost exclucively.

I've always referred to it (and used it) as a change pocket, as have jean manufacturers.