The PS3's lifespan has the potential to be significantly longer than the Xbox 360s. It's selling at a faster rate overall and it is just a more advanced piece of hardware in general.
The PS3 will see a steady amount of sales as Blu-Ray adoption grows and takes over the market. Sony can still package the PS3 as a nice Blu-Ray player in the future.
While I think it will be very, very close. I think assuming both consoles are released for the same amount of time, the PS3 will win the battle of sales.
And no the generation doesn't end when someone releases a new console. The PS2/Gamecube/Xbox generation is still going on. The winner is clear cut at this point though.







