Yes, but Valve is looking to change that with SteamOS and SteamBox. Hopefully they will be able to break the hold that Microsoft and Sony have on gaming and create an open, flexible platform that offers cheaper games and better graphics. Mobile phones and tablets have been evolving at breakneck speed because they're flexible platforms - there is more innovation and more competition. It doesn't make sense to have consoles with eight-to-ten year lifecycles.
Why not. I'm perfectly happy getting a console that will last that long. I don't want to spend money on hardware more often. If I did, I'd be a PC gamer. Which brings me back to my other point about how consoles and PCs are two different ecosystems that can coexist perfectly fine together.