"The chaos surprised many security watchers because Microsoft issued an update in March that patched the underlying vulnerability in Windows 7 and most other supported versions of Windows. (Windows 10 was never vulnerable.)"
So I don't really know what you mean by 'hoarding the fix'. The patch was not initially released to some OS versions because they are NO LONGER supported.
I believe the "hoarding the fix" comment was in reference to the patches for Server 2003, XP, and Windows 8 that were released publicly for the first time over the weekend (but had been distributed previously to customers paying for custom support) [0].
