I make my living writing software for the enterprise. If Unix and Windows was all there was life would be really easy. The Enterprise is better defined as the hodgepodge of systems acquired over time running a mix of purchased and proprietary mission critical software developed internally by the local IS department. Sometimes using proprietary gateways. Almost nothing is ever replaced, or thrown away.
Network topology is usually a mini-internet.
A whole host of different networks tied together by gateways. Much data communication among systems and applications is still performed in batches using scheduled processes. Windows NT has little hope of invading this environment in any significant way in the near term. These systems have extremely high availability requirements and are often not rebooted more than once or twice a year. It will take over 10 years of burn-in for NT to gain the trust of people who operate these kinds of systems.