Also, you are neglecting miners who consider the extra electricity as their investment capital and the bitcoin they earn as the asset they buy with that capital. For that portion of the miners no USD funds are needed on the exchanges.
I already said this elsewhere. Those miners that choose not to sell their bitcoins are in fact investing that cost into bitcoins, same as if they directly bought them on an exchange.
So, for each new created bitcoin to be "exchange neutral", one of two things must happen:
-somebody must buy some (significant) part of that coin from the miner, so miner can pay his costs
-miner itself must pay this cost
In any case, a fresh money must come from somewhere.
