What matters in giving the derivative currency units par value to "the real thing" is the lender's ability to maintain liquidity by having a (central) lender of last resort, not the (in)ability of secondary borrowers to print them.

There really is a difference between what would happen if people started demanding real paper USD as payment (i.e., just print more for the right banks) vs. what would happen if people started demanding real BTC as payment.