There is a psychological barrier because milli and micro sound 'small'. People don't want to hand over a whole wad of greenbacks and receive micro-bitcoins. I'm a fan of using uBTC but just referring to them as 'bits'.
Are there people who think "I've got 50 bucks! You know what, I've a notion to buy some bitcoins. How much would I get? Oh no! Only 83 millibitcoins
I guess I just won't bother."? I guess there might be, but it's presumably a fairly small demographic.I sell to a guy thru localbitcoins.com who fits that description. He is by no means a high roller and he buys around $100 worth each time, he is a pizza delivery guy but he moves some loot into BTC when he can afford it.
They are out there, not everybody is completely clueless about math.
and on the metric system topic... my god what a sad state of affairs that "Americans think metric is too hard" it is a base ten COUNTING system. It is literally the easiest system for humans to count and if they really are too fucking stupid to move a goddamn decimal point their fuckin smartphone will do it for them.
I'll be back, I need to go smash my head into a wall for a bit (or maybe a megabit) while I contemplate whether there actually is any particular reason for the existence of humans.