1 year head start may not be enough this generation to hold off the all conquering PS3 sales juggernaut from outselling the 360 when it matters most.
Maybe 18 months or 2 year head start will be needed to outsell the PS4 next generation. Providing there is a new XBox.
Microsoft have made a lot of mistakes this generation. 360 is choking under pressure when it matters most. Believe me outselling your nemesis in Sony means everything to Microsoft. To lose from a year's head start and a much cheaper console system than its rival would leave a bitter taste in the mouth of Microsoft executives.
The last 5 months has seen a huge shift in sales momentum between the PS3 and 360. The PS3 is totally whipping the 360 in weekly sales. Microsoft's last hope lies in Natal of extending the 360s lifespan and clawing back lost ground from the PS3 in market share.