The difference being that USD doesn't pretend to be pegged to anything. My point about MakerDAO is that the development team is claiming the impossible is possible.
One of the many aims of US monetary policy is that USD doesn't lose too much purchasing power too suddenly (eg no unexpected hyperinflation). Of course any currency from a decent country would aim for this kind of soft peg.
I guess you're technically correct that their marketing material claims to go beyond this in a eay which is technically impossible
