Let's compare:
Dragon Age: Origins
XBOX 360
Week 1 - 335,941
Week 2 - 173,230
Week 3 - 96,340
Week 4 - 134,460
Week 5 - 107,755
Week 6 - 121,373
Week 7 - 153,855
Week 8 - 180,681
Week 9 - 74,823
Week 10 - 35,007
PS3
Week 1 - 155,660
Week 2 - 72,304
Week 3 - 80,920
Week 4 - 77,414
Week 5 - 59,219
Week 6 - 63,881
Week 7 - 76,906
Week 8 - 89,604
Week 9 - 44,035
Week 10 - 22,415
Dragon Age 2
XBOX 360
Week 1 - 392,508
Week 2 - 128,897
Week 3 - 61,735
Week 4 - 40,841
Week 5 - 26,630
Week 6 - 19,569
Week 7 - 15,939
Week 8 - 12,506
Week 9 - 6,416
Week 10 - 4,938
PS3
Week 1 - 163,410
Week 2 - 61,210
Week 3 - 35,455
Week 4 - 25,976
Week 5 - 18,489
Week 6 - 18,111
Week 7 - 15,736
Week 8 - 10,917
Week 9 - 6,907
Week 10 - 5,347
PC
Week 1 - 148,830
Week 2 - 38,002
Week 3 - 26,165
Week 4 - 16,082
Week 5 - 10,850
Week 6 - 9,551
Week 7 - 9,002
Week 8 - 5,723
Week 9 - 3,965
Week 10 - 3,002
In total DA2 hit over 1.3 million sold during its 10 week run, mainly supported by the 400.000 Pre-Orders they had (with the Signature Edition only being available if you Pre-Ordered 1 month before release, otherwise you'd have to pay for DLC), but DA2's Week 2 was already showing a dramatic decrease in number of copies sold over all platforms in comparison, as apparently bad Word-of-Mouth got around, Week 3 is an all-time low and shows less copies sold than in any of the first 9 Weeks of DA:O, in fact DA:O's sales increased significantly after its first 3 weeks (see links below) as good Word-of-Mouth got around.
If the trend stays it is highly unlikely that DA2 will have more than a total of 2 million copies sold over its total lifespan.
PC sales aren't exact/aren't available for DA:O and probably don't include Digital Distribution though I wouldn't think that would show a dramatic increase in numbers.