Yeah, that 1 Million in 3 Months was in NA alone, and just on Wii. Add up sales from Japan and Europe and you get a very similar, if not a tad higher number than 3 mil in ten weeks.
And being a launch title can also go against sales. While Gears had over 10 million 360 owners to be purchased by,
TP had less than 5 million to sell to. Yes, it didn't have much competition, but how much did Gears have on the 360 at that time?