The same as it's always been... full integration with the entire line of business-oriented Microsoft products (including Exchange) and support for the vital third-party software that requires Windows.
For many years, Microsoft's business model has been to promote a Microsoft-centric universe. If you use Office, you'll get the best service with an Exchange server, which must run on Windows Server, and really needs Active Directory, which supports your Windows workstations, which integrate with Office. It's not just that Windows is a GUI-based OS. Microsoft products are a part of a whole tangled mess of dependencies, and for years we've been stuck dealing with the downside of that glorious integration.
Every IT admin has a story about the vital business process that involved a human robot. Every day a human logs in, and runs an Excel macro to generate a spreadsheet, that he saves as a CSV file and loads into a third-party program, which generates a RTF document, that needs to be renamed to
Sure, we had some old tricks... Batch files, DDE, COM, OLE, WSH, VBA... but they never really enjoyed full support from Microsoft. They were supported features, but not supported enough that third-party vendors would feel pressure to support any automation.
Now, with PowerShell and the Core offering of Windows Server, there's the notion that everything should be able to be automated. Sure, we've had that idea from the very first days of Unix, and *nix has embraced the concept to maturity, but *nix still doesn't run every piece of business-critical third-party software. For those of us who are already firmly entrenched in that Microsoft-centric world, this is a much-needed good omen.