I distinguish between proprietary apps and proprietary kernel. The open source world can build its own apps. Mostly. However, it can't build its own kernel if the hardware is undocumented and/or only supported by OS-specific binary blobs. Drivers are key to a lot of things.
MS is a lot more open-source friendly, and smarter, but it's pretty clear that this is a strategy to get more people tied into ecosystems which favor proprietary Windows. MS is behind, so they're playing catch-up.
I don't disagree, and I'll add that the Raspberry Pi is still encumbered by a binary blob that is required to boot, no matter the actual OS that is loaded after. I for one would absolutely love to see a 100% fully documented, Free and Open Source development board, from the board layout, to the CPU/GPU design, the boot code, and all kernel and userland software.
Unfortunately there is no real market interest for such a device, so I'll take what I can get.
MS is a lot more open-source friendly, and smarter, but it's pretty clear that this is a strategy to get more people tied into ecosystems which favor proprietary Windows. MS is behind, so they're playing catch-up.