I don't buy this 10 year life cycle business. Or at least, I don't think people usually take the phrase to mean what it actually means.
The Playstation 2 is still limping along. Sony, a few years back, stated they were on track for a 10 year life cycle for the PS2, the same as the PS1. Which if you'll remember, also managed to limp along for a while after the PS2 launched.
That 10 year life cycle doesn't mean the amount of time between new consoles coming out. It means that time, plus the amount of time that the older system keeps on kicking.
Now that said, I don't really think we're getting a new 360 next year. Maybe something akin to the slim models that Sony pumps out a few years into their consoles' lifespans. But I seriously doubt we're going to be waiting another five years for another XBox or Playstation or Nintendo system.