And this is where we part. Apparently you and I have radically different notions of 'games running properly' on a tablet. What you consider as 'some developers might decide to go further' has been proven by Apple to be the very fundamental of successful tablet/touch-screen ecosystems. It's not optional in any way. You can technically neglect it, but that'd result in a badly designed software. So much for the AAA games.
You have to understand that Windows has already a huge user base, and all the new notebooks, netbooks and desktop computers will be selling with Win8 on it. Many old time users will also upgrade their existing computers to Win8 (this time it's also easier, since the system requirements haven't increased). Windows app store isn't just for tablets, it's for all Windows computers.
Now if you are designing a Win8 metro application to the Windows app store, you should expect that almost 90% of your user base will have just mouse + keyboard connected to their computer (at Win8 launch). If Win8 tablets become really popular, maybe in a few years we will have 50%/50% distibution, but this is just a guess game and not something you should rely on if you are spending a lot of money in developing a new game to the platform.
Here is a link to the Microsoft guidelines for Win8 user interaction:
http://msdn.microsoft.com/en-us/library/windows/apps/hh465370(v=VS.85).aspx
I picked one line from the documentation:
Touch-optimized applications must support efficient and intuitive mouse and keyboard interactions that expose equivalent functionality
Win8 is not equivalent to iOS and Android. You cannot design apps to it that only support touchscreen control. Those apps will not even pass the certification process. If you browse the Metro developer site a bit more, you will also notice that Metro apps have native support for Xinput API to control your games with a Xbox 360 controller. Metro also supports the Xbox 360 sound API and Microsoft also brings full Xbox Live to PC with Win8. I personally think all this was done to attract Xbox 360 developers to port their products to Win8. Microsoft has a huge developer base developing top quality games for their other products (Windows/PC & Xbox 360), why not use this resource to bring top quality entertainment to the tablets as well?
It will be interesting to see how things pan out. The platform will surely attract console developers (Xbox 360 APIs and Xbox Live), PC developers (full backwards compatibility of existing DirectX games) and handheld/tablet developers (touchscreen input). Lets see who will adapt to the platform best. I personally predict that games that are very natural to control by all the three possibilities (touch, kb+mouse, gamepad) will be the ones that will be the most successful.
Fine for what? Do you have any benchmarks of a 17W SB that we can use for comparison?
There's plenty of Macbook Air reviews around the net. It has the same 17W i5 2764M as the Samsung Slate. Some previews compare performance in Windows 7 as well (installed with Boot Camp). Gaming performance in general is better under Windows, since GPU manufacturers have spent much more time in optimizing their DirectX drivers.
Now this is just speculation (or extrapolation if you want to use that term): Top of the line (four core) Sandy Bridge parts have 95W power consumption. Top of the line Ivy Bridge will have 77W. Now is we assume that the 60% faster GPU and 20% faster CPU figures apply to the top of the line (like you previously estimated), we can calculate a rough estimate to the power consumption to the energy efficient models as well. 17W * 77/95 = 13.7W. Also in this estimate I assume that power usage grows linearly as you scale clocks. The growth is actually more than linear, so this linear estimate is likely too conservative (the energy efficient chips likely consume even less). Now if the manufacturerers are happy with the 2764M perfomance, they might instead opt for lower clocked Ivy Bridge products. Now assuming linear dependence of clocks to performance, a 20% down clocked Ivy Bridge should have equal CPU performance to a 2764M with similar specs and 28% higher GPU performance (1.6*0.8). This would bring (linear estimate again) power consumption down to 10.9W. But as all these linear estimates are conservative (clocking CPU up doesn't bring linear gains in performance, and brings more than linear increase in power consumption), it wouldn't be a bad estimate to hope for a 10W Ivy Bridge that has slightly more powerful CPU and around 30% higher performance GPU compared to the 2764M.
Look at the iPhone. Apple has increased it's GPU performance by 5x every year (two years in a row), and the battery life of the device is still the same. Intel has the most advanced manufacturing processes in the semiconductor industry. It's not hard to believe that they reached 60% increased performance + lower power consumption in their newest chip design. Intel is telling us that the new tri-gate 3d transistors alone would halve the power consumption and allow up to 37% higher clocks. Add in all the improvements they have implemented to their next generation GPU core, and the 60%+ performance estimate starts to looks a bit conservative, and clearly indicates that power efficiency was a bigger goal for Intel this time.