Well, as a matter of fact, Windows NT has always been "POSIX compliant". In order for MS to sell to the government, they were required to make it POSIX compliant. Now, granted "POSIX compliant" is a very loose term, and there probably aren't many complicated POSIX apps that would actually run, but this is due to the fact that Microsoft has had no demand for better POSIX support. If the consumers or developers really wanted and asked for it, then I'm sure MS would update their POSIX implementation.
Well, as a matter of fact, Windows NT has always been "POSIX compliant". In order for MS to sell to the government, they were required to make it POSIX compliant. Now, granted "POSIX compliant" is a very loose term, and there probably aren't many complicated POSIX apps that would actually run, but this is due to the fact that Microsoft has had no demand for better POSIX support. If the consumers or developers really wanted and asked for it, then I'm sure MS would update their POSIX implementation.