I think the key is that this is not a VR device but an AR one. The illusion is harder to maintain in AR but if you manage it is way more tricky. The difference between VR and AR is undervalued in the discussion. imho, the ability to do a credible AR (due to superior computational power and the abundance of sensors) _could_ be the key for Vision success
Except it's not really--in the sense of an out-in-the-world-walking-around HUD. And certainly the keynote emphasized in-home entertainment and (I think?) gaming. It's got elements of AR to it but it seems much more like VR+. (And Apple was almost certainly smart to just coin their own term.)
