I don't think Microsoft really thought about the server market until NT4 came out, and people started using the "desktop" version on small servers....

However, the Unix business was a huge mess at the time. First, the all vendors were at war with one another, then they divided into two warring camps (SVR4 vs OSF).

While they were busing fighting one another, Microsoft nicked their cheese.....

Update: Of course, Windows NT was designed by the same guy as DEC's VAX VMS, so it's got that in its DNA. Maybe he was thinking of servers as well...