A couple of references to the use of the term "day one" regards PS3.
http://www.bit-tech.net/news/bits/2006/11/10/PS3_to_get_firmware_update_on_day_one/1
http://www.siliconera.com/2006/10/03/playstation-3-launch-games-in-japan/
You can also find comments from the Common Man referring to 'day one' activities. It's not a new phrase. MS have just focussed on it instead of 'launch' because their box is called the One, but people using the language as they have done for years clearly isn't being influenced as a result.
I forget the the XB is the 'one'. In my head it's now stuck as the Xbone or the 180 not XBox One!