I'm afraid there's more to it than you think
First off, you can't actually buy less than a certain amount of Bitcoin. For example, at Bitfinex the minimum you can buy is 0.004 BTC at the moment which amounts to approximately 16 dollars at current prices. Indeed, the world doesn't end (or start) at Bitfinex (though things are not a lot better at other places), but then there's another catch with Bitcoin fees (which may well be a catch-22). These fees are definitely higher than a US cent (let alone many times lower than that). In this manner, even if Bitcoin is infinitely divisible per se, the transaction fees make smaller purchases impractical down to outright impossible, with the implication being that it is in fact a question of affordable