First.. I think high end PCs will be more powerful than consoles by the time the PS3 launches.
Which is why the 360 launch was so important to be done 'early'. When it launches, it will reign supreme for about 6 months or so. After that? High-end PCs will have overtaken them.
As far as the 6800 Ultra (or whatever) never being used to its fullest abilities.. Why not? Sure, the venerable 9700 Pro wasn't used to its fullest abilities for a long time, but it sure is out of place now, isn't it? And somewhere between now and "back then", wasn't the 9700 Pro being pushed to the max? Of course it was. Unless you upgraded "too soon" to a 9800XT, and even then.. if you sold your 9700 on Ebay, then somebody was probably using it and pushing it to it's max.
I do agree on the point that the multi-core, multi-processing aspect of these consoles will keep them alive longer, because it will take developers longer to learn how to actually use the power of the console.
But, in all truthfulness, one of the reasons I'm so excited about these new multi-core consoles is because PCs will be going multi-core as well. And once that happens, it's essentially "all over" once again, as the PCs will have the upper hand due to upgradability.
Finally, I don't think it really matters to anybody but a handful of technogeeks if the PS3 comes with a mouse & keyboard & linux or not. What MS learned with the TVPC or whatever the name of their stupid product was, is that people don't enjoy consoles and computers in the same way. Even if both are being used to play games.
The console/PC experiences are completely different. Not only in terms of the different styles of gameplay, but in terms of the environments and situations which they are used.
Now, I'm one of the few people who have a HTPC which is also my gaming PC which is hooked up to my HDTV and sits in my living room. Both my Xbox and my PS2 are connected there as well.
But I'm single, I'm a tech-geek, and most people don't have the same priorities/interests/time/money that I have. And on top of that, I still have a PC set up in my spare bedroom that I do all other sorts of "PC" stuff on it.. like spreadsheets, word processing, and even playing an occassional RTS or FPS.