[acadien]

I'm not sure that mach and pH are units per say. pH for example is on a nonlinear scale and mach itself is unitless. Maybe that's totally irrelevant.

I guess its fruitless to try and apply logic to language and better to just accept the general usage?

[vacri]

You may have nailed it - apart from 'area 51', which is a proper name (and whose order I messed up to make the joke, unfortunately), the others are all ratios, not discrete units.

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 :)