The source is Gamestop and it says 'shipped'.

http://www.gamespot.com/articles/xbox-360-sales-reach-80-million-units/1100-6415644/

What? It's MS internal figures, and yeah course it's shipped.

Source is Microsoft - http://news.xbox.com/2013/10/xbox-360-sept-npd

Thats... Quite bad. Wonder why Brett aint done anything to change it.

Edit - 

Yeah. Sold to retailers, not consumers.

Pretty good for MS. Being the underdog and only their second generation. They have done a lot right with the 360 so far and really turned it around from the RROD at the beginning

You might want to check your numbers, if Microsoft annouced their total shipments as of the end of this quarter then you are missing the week of the 5th of October from your data, and if MS's 80m was as of the date they released the statement then you are missing two weeks worth of sold data, so no there's not 1.55m on shelves.

No one predicted 100M for Wii U too in 2005, or that all 3 consoles will be very close to each other either.

No idea how long since an official price cut, but the console has been cheaper to get than its last price cut

I think that X360 is tracked right in VGC, 1'55 million on shelves is probable. But ps3 could be easily overtracked.

The 360 is far from tracked right. 1.55 Million on shelves is far from probable, when the console itself is only selling an average of 55-80k over the last couple of Months (going by VGC numbers).

What 1.55 Million on shelves would suggest is over 20(!) Weeks of stock in stores/ on ships, right? Thats simply not gonna happen. Retailers wont order so much stock when said stock isnt selling.

360 is evidently undertracked by over 2 million outside of the US.

Well, maybe 1'55 million is too much, but other times it's been around 1 million this period of the year, so i just said, that is "probable" but not certain.