For once I agree (somewhat) with Tretton and in fact have been saying this for a while. The Wii U does not necessarily start a new console generation. It's just this gen part II for Nintendo, similarly Kinect/Move was this gen part II for Sony/MS.
If the Wii U tablet really takes off (unlikely) Sony / MS will just copy that. No need for new consoles - yet.
I also don't think prettier graphics are going to win anything for anyone going into a new gen. No matter how much more powerful the only significant difference will be true 1080p (which Wii U has and we don't care). Better lighting, more background details, more lifelike hair/clothes - who cares really?
The real threat to Sony/MS is cloud gaming and how 3rd parties would run to embrace that (one system - all homes!). Apple's icloud could be very threatening if Apple decides to enter the home gaming market (moreso than it is with tablets).