That'll teach me, I guess, for taking photos near Area 51 :)
I guess its fruitless to try and apply logic to language and better to just accept the general usage?
On the other hand, it's also worth noticing that scientific units come from science, but monetary units come from finance. The regularised SI system is only a couple of hundred years old, and ledger entries are much older. My guess is that merchants in ye olde Europe had to deal with a variety of currencies, and putting the currency first was convention. It may have also made it clearer in a manifest as to which column was cost and which was amount, in an era when weights and measures were highly varied. Absolutely no supporting data for this, just a hunch :)