To be fair the Wii was impossible to find in the same timeframe. I dont think the PS4 will keep pace in year 2 (Wii was just silly in 2008...) but I think the PS4 will not hit a wall and die after year 3 like the Wii.
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