Microsoft dropped support for DirectSound3D. OpenAL remains unaffected, and they can't do anything about that because it's not an API they have control over, unlike the DirectX suite.
That's why wrappers like ALchemy, DS3DGX, 3DSoundBack, etc. are capable of "restoring" DirectSound3D support under Vista onward in the first place; they just wrap the DS3D API calls into OpenAL, much like one might wrap old 3dfx Glide calls into Direct3D or OpenGL for older games that only supported 3D acceleration through Glide.
That said, I still don't get why they bothered to remove DS3D in the first place, and I also don't get why game developers didn't continue to keep using OpenAL in its place.