It sounds like you're still thinking of a console as a box that just plays games, a situation that is fast coming to an end.
Perhaps. Although, when you look at the last 8 years (this generation) and consider what may happen in the next 2 years, it's easy to see why:
People are not buying high-end "set-top-boxes" that happen to do a lot of stuff, among other, playing games - they are buying "game consoles" to play games, with some features of the console that go beyond gaming. There's a difference.
You don't sell your console to 50 million gamers and then suddenly think that those 50 million will automatically buy your new set-top-box that happens to share the same name. All else considered - when next generation starts, for the most people outthere, the next Xbox and the next PlayStation will be viewed as game consoles with extra features.
This might be changing, but it hasn't by much so far - and I'm still having a hard-time imagening what features outside of gaming that should make the newer consoles attractive multimedia boxes that would make people stop viewing them as machines predominantly for gaming.
There's also the point to be made that these other features don't bind the costumer to the platform. If a costumer uses the set-top-box to watch movies, listen to music, view pictures - it's as replacable as any other piece of CE electronics outthere. The only thing that will bind a costumer to their platform to some degree is building up a friendly software-eco-system, one like Apple has for its i-devices (iPhone, iPad etc) or Google has for its Android devices. Buy software that will also run even when you replace your old hardware with newer one.
The only thing is - what software do people want to run on their set-top-box / TV? An email client? A fancy picture viewer? Beyond games, I just can't think of anything else really, now that tablets are becoming popular and probably already found in many households, replacing the PC for basic surfing, emailing and showing pictures. And because games are still the predominant aspect of what the game console will do - the
stackable hardware argument with iterating consoles is relevant - and especially, how well it runs games.
If we have the scenario that Microsoft is going with a forwards-compatible platform and Sony concentrates on the 'traditional' console cycle, it'll be interesting to see how they compare to each other.
For one, I question how game developers tackle the "lowest-common-denominator" issue when they have 3 iterations of hardware to consider like -tfk- pointed out and with that in mind, how version3 games compare to effectively games running on your nearest competitor on fixed but older hardware when they have the version1 hardware to consider.
IMO - it would make more sense to have two APIs - one for forward compatible software (like mini games and software that extend beyond gaming that push your box to be more than just for gaming) and the other for games that need to compare well to your nearest competitor. I don't think you can have both at the same time.