I think that's a technicality. From my perspective 100% discount is called "Free", and I get that a few times a year when flying (tickets, upgrades, etc)

I calculate 100% based on the amount I get from my preferred airline for paying cash for groceries (0) vs the amount I get by using a card they issue (a few imaginary points/$). Then I trade those points for things I couldn't have had by paying cash. As long as I don't pay interest, we're in "Free" territory.

And as a merchant, yes it's annoying, but it's also nice when a customer pays with a credit card, because we actually get paid then.