We have heard for a long time that X1 were ahead of X360 as the most successful Xbox ever, but been some time since MS never said that again so I suspect that it may have fallen behind.
So I done some verification on VGC and have some preliminary data (I couldn't find full weekly tables for easy construction) that suggest X1 have been left behind.
X360 3 Years+launch WW = 27M 4 Years+launch= 37M
X1 3 Years+launch WW = 28M LTD = 31M (possibly won't reach X360 anymore)
X360 3 Years+launch USA = 14M 4 Years+launch = 21M
X1 3 Years+launch USA = 16M LTD = 17M (will probably be overtaken in USA this year as well. been severily down YOY and I don't think X1X will reverse it).
duduspace11 "Well, since we are estimating costs, Pokemon Red/Blue did cost Nintendo about $50m to make back in 1996"
http://gamrconnect.vgchartz.com/post.php?id=8808363
Mr Puggsly: "Hehe, I said good profit. You said big profit. Frankly, not losing money is what I meant by good. Don't get hung up on semantics"
http://gamrconnect.vgchartz.com/post.php?id=9008994
Azzanation: "PS5 wouldn't sold out at launch without scalpers."
