I disagree completely and categorically. Anything above 5 years for a console generation is pushing the limit and choking innovation. It's been 10. T-E-N. YEARS.
You are missing the point of consoles. Firstly, Sony and Microsoft don't even make money on consoles, they lost money on every unit sold. Because of that, it's really hard to sit on your comfy couch and demand that they ever make a new one, because they can only afford to do that so many times every decade. Like once.
Furthermore, consoles are designed to be budget systems. If console gamers had the resources to buy a new $700 system every few years then they would just be PC gamers. A console was intended from the very start to be a buy once, have "forever" type thing. That's why it takes forever for a new generation.
Sony and Microsoft are going to wait until they can pack a major punch into their new system. The new system has to be so far ahead of the previous one that it allows for entirely new gaming concepts to be implemented. Secondly, they have to wait until the limits of their console has been effectively maxed out to the point that gamers are getting bored with it.
Gamers, I said. Not you, specifically, but the market. Console games are still immensely popular and there's not a lot of pressure on games like Assassin's Creed or Uncharted to be released on a next-gen system. As long as games like that are successful and reaching their potential on the existing platform, then the existing platform remains.
That's the whole point behind a console.