Yeah, there were even efforts to make factory-pressed "BD9" BluRay-on-DVD discs a mass produced cheaper alternative when BluRay was being launched, though it never actually went anywhere. They kept the format though just because it made sense to give people a way to make home media without having to spend an arm and a leg on blank discs.
That said, the "requirement" for players to support BD5/BD9 has been dropped as of a few years ago, not that all of them did in the first place. Most players still support it, but you can't count on it.