Let's take another look at the wording Microsoft used in the SEC filing (emphasis added):
We derive substantial revenue from licenses of Windows operating systems on personal computers. The proliferation of alternative devices and form factors, in particular mobile devices such as smartphones and tablet computers, creates challenges from competing software platforms. These devices compete on multiple bases including price and the perceived utility of the device and its platform. [...]
Even if many users view these devices as complementary to a personal computer, the prevalence of these devices may make it more difficult to attract applications developers to our platforms. In addition, our Surface devices will compete with products made by our OEM partners, which may affect their commitment to our platform.
It says "devices," not tablets.
Now let's jump to a post made yesterday on the Official Microsoft Blog by corporate vice president for corporate communications, Frank X Shaw (emphasis added):
Fast forward a week, and head back to the West Coast – Los Angeles, in fact – where we showed off some new hardware muscle with the introduction of Surface, our new family of PCs built to be the ultimate stage for Windows. That event was certainly a kick…
That "our new family of PCs" bit certainly gives me the impression that we're talking about more here than just a few tablets.
It seems that Microsoft is doing everything it can to annoy and upset its hardware partners. Not only did it take on the job of building the Surface tablet with an as-yet unnamed OEM, but the company has also been working furiously to decouple Windows 8 sales from flatlined PC sales by pushing Windows 8 upgrades hard to existing PCs. The power that the OEMs once had seems to be dwindling, and that leaves Microsoft in a position where is has to pick up the slack and start selling.
If Microsoft does indeed enter the PC market not only with tablets but also its own desktop and notebook -- and maybe even Ultrabook -- systems then it's putting its weight behind Windows 8 like it has never put behind an operating system previously. And that will undoubtedly upset the OEMs.
But so what if the OEMs are upset? Where exactly are they going to go to find an operating system to replace Windows?
There's also no real demand for Linux on desktop or portable systems from either enterprise users or consumers. While Gabe Newell, co-founder and managing director of the video game development and online distribution company Valve, has plans to make Linux more attractive to gamers by releasing a few games for the platform, but it's hard to see that having any real, long-term effect. Although if Valve can get its top games running faster on Linux than on Windows, that could bring the hardcore gamers over to the platform and encourage OEMs to offer performance Linux systems.
Microsoft understands that it may upset its OEM hardware partners, and while the steps the company is taking may indeed affect OEM commitment to the platform, there's not an awful lot the OEMs can do about it. It seems that they are more reliant on Microsoft than Microsoft is on them.