I think the idea is the return on most factories is zero! anyone who invests medal fold into factories is basically a fool. the amount of gold from medals is so low that it would take years and years to get a profitably factory
well the return on training grounds is not too bad but it is also near zero if you have them all fully upgraded, well which taxes 400 gold or more. which getting that much gold would take forever from medals as the above poster pointed out.
so using gold from medals for what most gold is used for would be a not so good idea.
using gold from medals to buy currency to buy weps, increases consumption! which stops some of the problems some loud mouths have been complaining about.
so having medals give currency one is more likely to spend the currency to buy foods or weps on impulse.
where as having gold from medals one would be more likely to upgrade a factory or taring center.
having medals give currency improves the economy in terms of items consumed!