They're not trying to design a one size fits all UI this go round. They did that with Windows 8, and all it did was make people get all frothy at the mouth. This time, the desktop is the desktop, a tablet is a tablet, and a phone a phone, but they all share the same underlying framework, and in some cases, can all use the same apps.
Or to put it another way, they're all running the same OS, but each one uses a different UI depending on what it's on.
And this will likely be a very strong position to take. I have a older Windows phone that is retired. And I loved using it. It was great. The primary issue that I didn't like was that I could only use programs written specifically for Windows mobile. And while it had versions of word, they were mobile versions.
I preferred the way the device worked. Even compared to today's iphones. But the segmentation of data and programs from their desktop counterparts was too significant.
If all windows devices run the same operating system, and therefore can exchange data seamlessly, and use the same software, then that is a very powerful combination.
As it is, it's to cumbersome to work with data and documents on the iPhone and then finish the work on a Mac. The tools are different. The operating system is different. The whole process is essentially using 2 dissimilar tools to work on the same document.
Now, if the primary difference between an iPad, iPhone, and Mac were size, then we'd use our favorite programs on all of our devices and our data would move seamlessly between them.
Microsoft also has the Microsoft accounts system which will unify your devices with the same preferences, favorites, and appearance etc.
So if your data is stored on the cloud for example, each device will essentially be the same, just a difference of portability.
Using tiles on the phone and tablets makes sense. But it will also be cool if we have the option of switching to the desktop view on our tablets and phones as well.
In the end, this could actually position Microsoft to crush Apple and Google in the tablet and phone market. Windows users installed base equals nearly 90% of the installed machines in the industry.
Those users having the option of all their devices being completely interchangible with their desktops is going to be very tempting.
Apple's market is going to appear very fragmented by comparison after this move by Microsoft. Users still on Snow Leopard, Lion, Mountain Lion, Mavericks, Yosemite, ios 6.x, ios 7.x, iOS 8.x, and by the ios 9.x.......
That's a lot of segmentation compared to Microsofts ambitious decision to unify every device on one version of Windows.
Apple is going to have a hard time matching this move with the way Apple has quickly obsoleted very powerful and relevant machines simply over minor issues like production year.
Compare that with Windows 10, which my 15 year old PC still significantly exceeds the system requirements to run.
Now that's closing a lot of fragmentation.
To even come close to this move, Apple would need to move all Apple devices, including iPhones and iPads to OS X. And then resume support of older macs as far back as 2000. Or at least bring all Intel based macs back into active OS support.
Apple will not be able to match Microsoft on this move.