@kurkosdr: Actually, Sony's a pretty bad example of this. The PS3 has been around for years - the "nextgen" systems were sophisticated enough to meet gaming demand for several years, subject to modest enhancements to try to compete with Wii, such as the PS Move and Kinect. And game development for those features has been slow, to say the least. (I *really* like Sports Champions for PS3, but that's the only game I've seen that really uses the technology to its potential.)
And even now, there's no *particular* call for a new console. I'm not sure what tech has advanced to the point that a new hardware loadout is needed. Few are waiting for the next generation with baited breath, because there isn't really a demand. The Wii U brings some new ideas, but I'm not buying it for at least a year or two, depending on how impressive it actually turns out to be.
Capn John: Actually Apple is a good example. Way back in the mid '80s, in the announcement of the Lisa, Steve Jobs blabbed about the Mackintosh (yes, <i>that</i> Mackintosh) he and his group were working on --- effectively killing the Lisa.