Any individual can do whatever they want. I'm not contesting that.

The point is, is that they are all already measured in USD because that's what the UOA is.
A UOA is not a personal thing. A UOA is what a *society prices goods in.*

The price of all commodities and all other currencies are set against USD. 
And if a pairing EVER deviates from that, traders jump in to pull them back in line.
Because there's a million traders waiting for a deviation to happen so that they can get fiat.