I think people overstate how long this generation can/will last ...
At this point in my life I can say that I have seen this pattern over and over again in multiple markets and it always seems to turn out the same. Because people have a habit of comparing things against what is readily available, and they see no reason to buy something else that is already available, they believe that nothing is on the horizon that would make them upgrade in the near future; eventually something comes out that is unexpected and surpasses what they currently have to such an extent that they see what they have as being inadequate.
An example of what I mean is ... Several years ago now, I had a friend who bought a 80GB (IIRC) iPod Video and was entirely ecstatic with it; and his only complaint with it was that it didn’t have an (easily) replaceable battery because he didn’t see any way they could make a better iPod. Unfortunately for him, Apple released the iPod Touch/iPhone within 6 months and he was replacing his (perfectly good) iPod after only owning it for one year.
When you consider that business class notebooks are offering more powerful CPUs and GPUs than are in the HD consoles, all companies have (probably) all been working on advanced controllers potentially to offer both more accessable and more depth in gameplay possibilities, and it is possible that companies are (probably) looking at ways to offer unique features (like 3D visuals off of a conventional TV) it is entirely possible that by the end of 2011 the same people who claim that they’re entirely satisfied by their current generation console will be lining up over-night to buy a new console.
As I have said many times already, I have my doubts about how effective Natal can be at extending the life of a console primarily because I have seen it tried and not work before (Sega 32x, Sega CD); and I believe that Nintendo released the Wii as a next-generation console rather than an add-on because they knew people wouldn’t accept a brand-new control scheme as an add-on. I fully admit it could be successful, but it has to be far more successful than any 5 XBox 360 games combined for it to have the impact people are expecting.