Microsoft isn't turning Windows into a walled garden -- but it might be a good thing if it did.
Last week, the co-founder of Epic Games, Tim Sweeney, wrote an angry piece about the walled garden nature of the Microsoft Windows Store, warning it was "the first apparent step towards locking down the consumer PC ecosystem".
There are many ways in which that's not really true: you can sideload Store apps, and you can build and sell Win32 programs and those programs can call WinRT APIs, so there's no need to worry about getting locked out from new features. Or you could create a Win32 program to put in other stores and to sell on your own website and also wrap it to distribute through the Windows Store using the Project Centennial bridge, so you're not losing access to any distribution channels.
And if you think Microsoft is only developing the UWP and WinRT framework for Store apps and nothing for desktop Win32 apps, what about DirectX 12 and all the non-Store games using it?
There may be some specific, technical issues that Sweeney is concerned about but didn't actually reference. He could be concerned about things like the WDDM 2.0 graphics and compositing pipeline, which includes a standardised rendering pipeline through the Windows compositing engine that reduces artefacts like tearing -- remember that it's only required for games sold through the Windows Store.
Some of the issues that gamers are concerned about sound more like bugs than deliberate changes (asked about some frame rate issues, Microsoft's Mike Ybarra noted on Twitter that "we will fix Vsync"). And while they're not speaking officially, devs from AMD's Radeon team and Intel's graphics team say the new compositing scheme makes sense and these are controls that belong in the operating system.
Less charitably to Microsoft, you could note that its grip on the Store isn't exactly tight; there are plenty of fake apps showing up there on a regular basis and app approval is almost notoriously fast and automated.
There have never been any stories about Microsoft refusing apps because they're too political (which Apple has done in the past). And if UWP is such a threat to every other type of software you can run on a PC, why is Sweeney pointing out that the Windows Store isn't as well populated as other games stores?...