This discussion is based of course on a preview release and various milestone leaks of Windows 8. Everything in Windows 8 is subject to change.
As it stands now, Microsoft has replaced the Aero start menu with the Metro-style tiles grid. This means that when you click on the start menu button in the Aero interface, you are shown the tile screen instead. To me, that means that the made-for-touch UI is tied in closely with the made-for-the-mouse desktop UI.
While the tiles screen is still usable with a mouse, it’s not optimized for it. But what is worse, because of the tight integration of both paradigms, will developers go through the trouble of designing a UI for Metro for their apps? Or will they just expect people to use the desktop version?
Where do you start Aero apps? Are they tiles as well? If not, then why have the tile window be the start menu, or will you be limited to the apps that in the dock? However, if Aero apps can be tiles, will this not be confusing for most users? Is the touch version of a specific app a different tile than the desktop version?
Apple introduced the iPad with zero backwards compatibility for OS X apps. They now have a thriving App Store and a decent selection of high-quality apps.
The reason that Microsoft is taking this route is that they want to hedge their bet on tablets. Their business is selling an operating system —and foremost Office. They don’t make money from the hardware. Still I believe the current solution is far enough removed from a true desktop experience that it may still end up shooting them in the foot, because people may hold off upgrades because of the heavily changed UI —think Vista.
This is of course heavily influenced by the idea that `It’s better to have no tool at all, than to have a bad one’. This idea, however, is essentially a compromise, and one which Apple often prefers over the compromise of an inferior product.
So, when Steven Sinofsky calls Windows 8 a No Compromise design —a statement high on marketing, low on realism— he means that `having no tool at all’ is a compromise Microsoft is not willing to make. They would rather have users tap their way through Office for the desktop, than have no version of Office at all —makes complete sense from their business perspective. This doesn’t mean, however, that Microsoft is not making any compromises at all, they are just making different ones.
Update: Although Microsoft seems to be working actively on a redesigned version of their Office suite. Still, there are tons of 3rd party desktop applications out there that still require the compromise of allowing touch for control.