As I've brought up ad nauseum in the thread, releasing a new console doesn't negate the fact that the 360 still has years of profitability. If a new console drops September of 2011, the 360 will still outsell the new console, month over month, for at least 12 months, and will have game support past that. The PS2 is still profitable for Sony, and this generation will have an even longer life post-new console release than others, as they can transition from being a gaming center to an entertainment center.
But you always have to think 2 years in advance in gaming. That's the average development cycle in most big studios, with the exception being annual franchises handled by the same studios (read: sports games). So when you think of it that way, you begin to see why saying that the 360 has years in the tank left isn't the right way to be thinking, IMO. I've used it as an example before, but Gears of War 3 is as good as this console can get. If you look at how it optimizes every square inch of available power, it's as good as this generation of Microsoft can get. You can also use Crysis 2 or Battlefield 3 if you'd like, although I like using single-platform games, as you know they were designed just for that system.
And, realizing that GoW3 is about as good as the 360 can get, you then realize that development started for it in 2008, after the launch of Gears 2. The engine is from 2008. The textures were in development in 2009. You don't see innovation for years down the road. So saying that 2013 is too soon for a new console, in reality, is saying 2015 is too soon for a new console, as that's when you're going to begin seeing games that are markedly better than this generation. The first games on the 360 weren't leaps and bounds better than the XB1, they just had a processor that could handle new animation techniques, specifically particle effects. It was a few years after launch where you started to get truly great games, from a technical standpoint.
If you remember the 360 launch, one of the big 360 titles was the Peter Jackson King Kong game. It was developed separately for both the XB1 and the 360, and it was used to show the vast improvement of the 360. Here's that game, if you don't remember it: http://youtu.be/IwEpz3LeZx8
And, speaking of those yearly franchises, here's Madden 06 on the 360: http://youtu.be/DWUclELibqQ
Advancements can't happen until developers get access to new limits. If you're a Madden fan, at this point, you're going to be paying for slight tweaks on Madden 10 until a year after the next console (so hopefully Madden 14). Although EA will definitely be on board early in the new console's development, so it's possible their first entries on the XB3 are an improvement.