At the time of the OP, in June 2008:
Wii- 25
360- 41
PS3- 15
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Today:
Wii: 51
X360: 61
Ps3:30
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So in the past 10 months they added (in rufly 1 year):
Wii: 26
X360: 20
PS3: 15
At least 2.5 years remains til next gen launches (Xbox 3), but games will keep selling well into next gen, probably 3 extra years (rufly 6 years).
So lets try to multiply the above numbers with the remaining 6 years:
Wii: 26x6=156
X360: 20x6=120
PS3: 15x6=90
Added with todays numbers, total number of million sellers will be:
Wii: 207
X360: 181
Ps3: 120