1. They probably derive from value from the vendor lock-in than they expect from sharing. The rival OSes can already join an Active Directory domain (some require third-party tools, some don't). Right now, if you want to manage a fleet of Windows desktops you need a few Windows Server licenses for your domain controllers---and the requisite CALs. There are already open source AD clones anyway, which is probably why 2008, 2008 R2, and 2012 functional levels have such nice new features. They want to maximize the number of Microsoft products you're using.
2. Until Microsoft storage demonstrates the reliability of EMC or Compellent, no one is going to care. Linux and Windows can both work as an iSCSI target, and that's good enough for people who want cheap, accessible storage. Customers who already demand reliability and performance are paying for it because they need it. Maybe there is a bigger market for people who could benefit from some middle tier of storage, but there are plenty of vendors in that range too. So, the question still boils down to "Why put that storage in a server and trust Microsoft to present it?"
3. At the enterprise level, if you're relying on AV detection to find malware, you're already behind the curve. Most of the new security features are targeted at the network-connected enterprise machines, with some trickle-down benefits for consumers. The VM/hypervisor idea will wreak havoc on the two performance areas that matter for Windows desktops---CAD and gaming. While I agree with the principle, it's not happening. Microsoft started research on Singularity almost 10 years ago, and little of that work has shown up in Windows.