I think the low end of the ps3 would be about 30 million. Because a negative momentum of developers abanding it could take place and kill sales till it hits 300$ or so, then it's momentum would be at xbox levels but with better support in japan.
If HD-DVD takes over as leader, then it'd really die fast. Europe&America wouldnt hit past 15M on brand alone at that point. When they stop buying they stop buying Fast over there. I'd give this about a 5% chance of happening.
360 - prob 40 million, on pure momentum at this point.
Wii, yea 50 mill is prob the lowest possible on how much word of mouth is helping it.