Microsoft is putting pride in one-size-fits-all... that is, the same system on Smartphones, Tablets, Cheap Netbooks, Desktops, Workstations, Webservers and Datacenter servers. The different editions are not that different.
A Windows server does not get much lighter than 30-40 GB of disk drive and 1GB of RAM. For companies with virtual machines, 10s, 100s or 1000s of them, significant amount of resources are wasted here. There are of course SAN-technologies to de-duplicate blocks, but this is both advanced and expensive. Many Windows servers dont do more job (create more value) as a web-server, light database-server, printer server, or an AD/directory server than a RaspberryPi with Raspbian can easily do. Storage requirements for Raspian is 1-2% of Windows Server!
Tablet buyers who buy an iOS/Android tablet with 64GB of storage more or less gets 64GB for their media. While an owner of a 64GB Windows tablet finds that not much more than 32GB is actually available to be used.
Even if Microsoft manage to keep their requirements at the same level for the years to come, they will still be much heavier than the competition, and in many cases it matters.