The Xbox360, PS3 and Wii have all (AFAIK) gone well beyond the lifespans of their predecessors. It's just taking longer and longer to recoup that investment.
When they came out they were much better (in price-performance terms) than their PC equivalents. As expected, this lasts no longer than 6-12 months.
Rumor has it that the next Playstation will be subpar compared tot he PCs of that time [1] (read the whole thing).
One issue with the PS3/Xbox style gaming is that we're hitting a wall when it comes to improved graphics. Graphics are getting better but not at a rate that people tend to care about. The bigger problem is that those improved graphics come at the cost of content creation (meaning it's more expensive to develop a "level" with more complex models, higher res textures and so forth). Games are getting shorter [2].
At the same time mobile gaming is taking off. Tablets (and possibly phones) are becoming the new consoles. The current iPad has 1GB of RAM and some pretty impressive graphics (given the form factor). And it's only getting better for the foreseeable future.
Mobile gaming I think will hurt Nintendo the most and I see a not insignificant possibility that Nintendo will end up like Sega and just be a software house. I seem to remember reading something about their investors questioning them not bringing their valuable franchises to iOS.
[1]: http://arstechnica.com/gaming/2012/04/the-x86-playstation-4-...
[2]: http://arstechnica.com/gaming/2011/04/the-incredible-shrinki...