Where does it end?
So how long until Apple are asked to provide competitors with access to APIs it uses in its own software? Almost every piece of well-known Apple software (Quicktime, Safari, iTunes) on the Mac uses APIs that aren't available to third-party developers.
I could use mobile phone manufacturers as another example, but the point I'm getting at is that OS developers have a set of private system APIs and a set of publicly available libraries providing APIs for third-party developers. The premise is that third-party developers use the safe, secure public APIs for their development, knowing full-well that doing so will yield reliable results. If they want to reverse-engineer the operating system and find there are methods they can use which might be more efficient then they're welcome to try, but don't go crying to the OS maker when those methods yield unexpected results or are retired/withdrawn further on in a product's life cycle.
I have to say that for many years (since at least the mid 90s when I started using Visual Studio) the MSDN library distribution supplied with Visual Studio has been leaps and bounds ahead of competitors in terms of the comprehension and examples provided. It didn't matter if I was making some simple application that processed and analysed data or if I was authoring a multimedia title using C++, I have rarely found fault with Microsoft's documentation of supported APIs.
Basically this new 'agreement' (if you can call it that when being bent over a barrel and forced to drop your trousers) paves the way for competitors to demand full documentation of the Windows operating system, covering many aspects of it that were never meant to be used by third parties in order to safeguard the operating environment. Next thing we know there'll be some dodgy antivirus developer who will demand that Microsoft provide full documentation for features that really shouldn't be tampered with.