Just looked at my old posts, I'll bring up a few things people probably don't know.
- In Japan, Gran Turismo 3 hit 1.7m copies when the PS2 userbase was at 5.6m. That's above a 30% attach rate.
- If a 30% attach rate seems unbelievable, look at Halo 3. In the US it was above 45%, now it's around 42%.
- See this post for details outside Japan.
Basically, as long as it can do well in Japan, and can keep around a 20% attach rate in Others/America, it may be able to pull it off (assuming the PS3 sells at least 45m consoles).
10 million is far from guaranteed, but it has a much better shot than people think. I just don't see how people can put its sales around MGS4, that's far too low...