Reasonable head-canon, that's not how it's presented in the setting books though.
I think it's just ill-considered, especially as there are historical examples, which I suspect the writers were unaware of. Japan shows what happens when you have big feudal-esque (I know not exactly sigh) society trying to operate whilst iron-poor. The iron age shows how iron as currency works. None of the lessons of either are evident in Krynn, it's just like "We're special so we'll use a different currency!", like the currency version of "Our elves are different!".
I'm not a metallurgist but I strongly suspect that, given how many kinds of steel there are, and how you need to use the right kind for the right job, you could not, in fact, easily use steel coins to make weapons/armour, nor easily melt weapons/armour to make steel coins. Iron would make a bit more sense.