The problem is asking that question. It is irrelevant when they products are fundamentally different. Its like comparing, well, apples & oranges. You cannot compare the methodology of a hardware launch (iPad) to a software launch (Windows 8).
You do not launch major pieces software without a beta / dev preview release. No one does. Even Apple doesn't do it - Lion, iCloud & iOS5 were released in 'unfinished states', which Gruber claims to abhor. So instead of comparing above mentioned software launches (in an unfinished state) to Windows 8 (also in an unfinished state), Gruber chooses hardware.
Compare the Xbox & iPad release schedules, and iOS5/Lion & Windows 8 schedules. I doubt you'll find that the hardware ships with a public beta. And I doubt that you'll find that software ships without a beta.Gruber is twisting examples to suit his arguments, and this is fundamentally flawed logic.