For hobbyist use you can just pick a random value and it'll usually work. Open-source hardware can get a product ID for free from https://pid.codes. Small-run commercial hardware can usually get a free product ID from the maker of their USB-capable chip. And once you're big enough that you're designing your own chip, $6,000 isn't such a big deal anymore.

So yes, you are technically right, but it really doesn't matter all that much in practice. USB is by far one of the most accessible major hardware standards out there.