PS4 sells 20 mil more than PS3, XB1 will sell 20 mil less than 360. So- PS4 100mil XB1 60mil.
XB1 will not do nearly as well in Europe as 360 (due to the only reason they even made a dent in Sony's deathhold was the price) and the PS4 will be more competive in NA (if not a close win). I don't see a lot of new gamers buying like what happened with the Wii last gen that's I why I see essential 20 mil in sales shifting to PS4 w/o them gaining many of the sales that Wii took last gen.
If your assumption is even 50% of the Wii owners who did not buy a PS360 will go with PS4/XB1 then I can see how you could assume around 100 mil each, but I doupt many Wii owners who did not buy a PS360 are going suddenly run out and buy a "core" gaming console now.
End of 2009 Predictions (Set, January 1st 2009)
Wii- 72 million 3rd Year Peak, better slate of releases
360- 37 million Should trend down slightly after 3rd year peak
PS3- 29 million Sales should pick up next year, 3rd year peak and price cut
