Honestly, the performance gap in this generation was driven primarily by Nintendo needing to keep manufacturing costs (super) low in case the Wii flopped, and needing to keep development costs low in order to encourage third party development and in case they were the only company supporting it.
As soon as you start approaching (and passing) the fidelity of HD games development costs spike and then hit a plateau because you're producing content at (roughly) as high of quality as we can produce; the additional time it would take to make a model for an animated movie is offset by the additional time it takes to optimize the model and textures for use in your game engine. What this means is that 'if you're in for a penny, you're in for a pound' and in the next generation it doesn't make sense (in terms of development cost and timeline) to hold back because you won't save any money in terms of development costs.
What I expect the next generation will look like (in vague terms) is all three console manufacturers will produce hardware that is as powerful as it can be and still be sold at a profit (or small loss) for $300 to $400; and unless the hardware is released more than 2 years appart the graphical differences between all hardware will be small and difficult to notice in game.
