Why not make it a 15 or 20 year lifespan. Thats how long TV's used to last for back in the good old days.
I believe the PS4 to be launched around the 6th aniversary of the PS3's life = late 2012. Maintaining a pattern of consoles overlapping each other as has been done in the past. However, if a new XBox was launched late 2010 expect the new PS4 to arrive late 2011. A two year head start would be too much of a head start. The new consoles will be far superior than the ones currently available.







