Actually... that argument would have merit. Coins aren't legal tender, and it's considered rude as fuck to pay for something in pennies (if the store will even tolerate it).

If there were sub-pennies, which'd be utterly worthless by any definition (really, a penny is worthless), and you tried using them to pay for something, a cashier would probably throw the coins in your face. It costs the store more money to have the cashier wait for you to count, and then to double-check than the profit from the transaction is worth.

Bitcoin kind of has this problem, in a way. In calculating fees, 1BTC is way more valuable than a hundred-million satoshis, which I don't think would even be spendable. Because of the cost to store that shit in the blockchain, it will probably never be spendable unless a bitcoin costs something like $1B each. In a way, bitcoins become less fundamentally valuable as they increase in price, because your average transaction amount is going to decrease, while fees for smaller transactions is more harsh than with larger transactions (or at the least, static). We need more scalability solutions in place (even if it is just a bunch of universities hosting the full blockchain as a public service in exchange for donations) before Bitcoin starts increasing the number of digits after the radix point and decreasing fees.