DuckTales used gold because . . . . children's cartoon.
The comics have always used "real coinage," typically silver dollars (there's an early Barks tale where, to compete with Flintheart Glomgold, they both convert their ENTIRE FORTUNES to silver dollars, put them in two separate piles, and whoever has the larger piles is the world's richest duck.)
Dammit, now I HAVE to restart my old Barks series from the original SD, don't I?