Pappnaas, your logic would seem to also dictate against Microsoft changing the UI so radically. Or, at least, removing the ability to change to a fully functional version of the more familiar Windows 7 interface.
No, Pappnaas's logic is correct. While Windows 8 may have a radically different UI, it doesn't prevent you from doing anything that Windows 7 could do. It just may do things in a different way. While the ARM RT version has restrictions, the normal x86 Windows 8 will run anything that Windows 7 can.
Backwards compatibly is a big thing for Microsoft. Windows 8 32 bit can run apps over 30 years old with no changes, no other desktop or small server OS even comes close to that. The only reason the 64 bit version can't go that far back is AMD's fault, not MS.
Also, part of my reasoning is based on the fact that MS seems determined to make us all use Win. 8 and its new interface. If they would go as far as they have, it is no real leap to some differences in networking compatibility.
Did you know that Vista/2008 and above use a completely different protocol from XP/2003 and below when sharing files? Did you ever notice any problems sharing files between say Windows 7 and XP? Probably not, most people don't. People don't know because they never noticed any problems, both old and new share files just fine. Again, backwards compatibly is a really big thing to Microsoft. It's a huge leap to think MS will break network compatibility.
I've personally tried the above situation and can confirm that Windows 8 can talk to OSes as far back as NT4 and 98 without problems.
Further, Win. 8 brings a new file system, ReFS. ReFS may not be implemented across all of the variants of win 8 at release, but MS plans to eventually spread it out to all versions of Win 8, for all drives. Now, with a mobile system, pad, laptop, or phone using the ReFS, how will the NTFS based Windows 7 PC be able to read the ReFS drives. It seems reasonable to believe that MS has included some means for compatibility, but that is not guaranteed. Maybe I have missed it, but that issue has not been addressed in the reviews that I have read. Also, the Win. 8 phones probably don't use ReFS.
ReFS is only on Server 2012, not any desktop or mobile versions. There is no evidence that MS want's to spread it to other versions right now.
N7SC, I don't want to offend you but your post sounds alot like the whole "Vista will DRM your files" scare crap from a few years ago. Windows 8 has lots of problems and Metro sucks on a desktop, but compatibly is not one of them.
Edit to include: Windows 8 requires a 1GHz processor that supports PAE, NX, and SSE2. It also requires a graphics system that is DirectX 9 compatible and has a WDDM driver. My laptop is okay with the graphics driver, but the processor speed is just a hair to low: the laptop is a 10+ year old HP Omnibook 6100 with a 933MHz Pentium III M processor. It does run Windows 7 (32-bit) just fine. Windows 7 never balked about the clock speed on installation. But if Win. 8 does a more thorough check of the processor speed, then it won't install. But, I'll likely try it out anyway.
A Pentium III supports neither NX or SSE2, so if Windows 8 does require them it won't work. Also, it's very unlikely for a P3 laptop to have a DX9 video card in it. A quick google shows the Omnibook 6100 as having a 16 MB Mobility Radeon, not even close to what is needed.