The other problem is that the name SFU doesn't convey posix as much as "interoperability with unix". Way back when, unix had a bunch of standards associated with it, posix was the original, since then, they've added a several "unix" standards.
Having Posix checked isn't as useful as it was.
On the other hand, all those posix-compliant linux servers that got soldm claim greater unix compatibility, are all very interoperable in the first place, at least, more interoperable for the money, than Microsoft's offerings. Microsoft doesn't appear to have had as much traction in its strategy to bind nis to AD as they hoped, so now they don't want to support SFU(adding new features,etc...) since it's mostly customers who if they buy windows, buy it at sufferance, and would not seriously consider replacing their unix with windows servers.
On the other hand, careful SFU management tuning and sizing might help people buy less windows, and run linux/unix alternatives in a couple of scenarios I can think of, so I'm not surprised Microsoft wants to stop subsidising something that doesn't meet its main goal(more windows server licenses with lock-in) and a risk of loosening the lock for highly technical clients.