The X360 had about 13 million consoles sold in September 2007 (Sep 2007 is when the Wii passed it, and the Wii had 13.17 million consoles in September 2007). The xbox did sell 528k units of X360s in that month (people buying X360s for Halo 3). Apparently Halo sold 3.3 million copies in the first two weeks in the US, so let's roughly estimate that they sold 4 million worldwide through September with an install base of 13.7 million. (End of november MS would say they sold 5 million units worldwide for Halo 3).
So, 4 million copies sold out of 13.7 million copies - pre Worldwide Economic Recession
At the end of 2014; MS had 10 million units worldwide. Per Ars Technica - you're looking at 15 million X1s worldwide. So...if you factor in a rough 10% decrease in median household income between 2007 and 2013 (US)..Halo 4 should be looking at 3.5 to 4 million copies sold to keep up with Halo 3's numbers (trying to generally account for the economic changes since then) as well as competing games (CoD + Fallout 4 + Tomb Raider + Battlefront).
Super interesting note: the numbers MS has used for Halo 3 and 4 implies have ALWAYS included hardware - they just didn't note it separately.
MS said for Halo 3 that it racked up worldwide sales of 300 million USD its first week (9-25-2007 to 10-1-2007) - but had sold 5 million copies world wide by November 30, 2007. Those numbers don't seem to match up if they are just games, do they?
I kind of think they've always been including the bundles in that "revenue grossed" bit - because they're comparing it to movies and book releases.
Based on the reported numbers for Halo 3 at launch, it seems unlikely it only included software. The hard worldwide numbers we got for Halo 3 launch were 5 million copies worldwide sold between 9/25 and 11/30 (2 months) - but 300 million dollars in the first week alone. If you wanted to establish a trendline, MS announced that Halo 3 had sold 8.1 million copies by Jan 3 2008. So in the month of December, it sold 3.1 million copies. So...even if you say 80% of the 5 million copies (4 million) were sold in the first week; you are looking at an average expenditure of $75 for each copy of what was a 59.99 game IIRC? That seems high, and I don't think people bought that many limited editions.