[grahamburger]

Thank you, my curiosity is sated :) I think the 'somehow' is pretty simple - I think they just provide their own CC number (or one they've assigned to me) to the merchant when I tap my card, and then charge me later.

Good point about the merchant specific CC points - it seems obvious that Google is losing out in this strategy because they're probably footing part of the merchant fees instead of passing them on to me (or the seller.) I couldn't think of a way that that would matter to me as a user, though.