MS isnt counting something.
We pretty much know exactly what Halo 1-3 sold through various NPDs and MS comments. Reach is not overtracked by millions of units.
These figures do not include digital sales as Reach was bundled digitally over 1 million times last holiday.
So basically all you people arguing the answer is simply we dont know what the 43 million is. Sony fans are teying to attack the number to make themselves feel better and MS fans are getting defensive. The fact of the matter is that really again we have no idea what its sold. Though I will say this is now the 2nd time that MS has released numbers that make the physical copy of Reach look overtracked so that may be a part of it.