The effect (see "antithetical") is the same, even if you're just passing on the costs that someone else is imposing on you, instead of capturing it all for yourself. That's one oversight in this response/rationalization. There's at least one other oversight (or possibly dishonesty) at play here.

That Postcard is merely passing on the cost of custom domains doesn't actually explain Postcard's pricing wrt this issue. If someone wants to use Postcard without having to use a postcard.page domain, they have to pay $8 a month, not $1.25 a month.