I can go on the Google Apps website right now and buy myself seats with a few clicks and a few minutes. If I want to buy Windows Enterprise licenses it will take weeks, cost an unclear amount (at the onset), and I'll have to talk/negotiate with pointless sales drones.
I worked for a startup, under 20 machines, I tried to buy then Windows 7 Enterprise. Microsoft's partners were super unhelpful, disinterested in a small account, refused to provide clear pricing, and I was getting upsold even before we got the basics squared away ("I'll just add on 20 CALs, a Windows Server license, and let's talk exchange!"). Ultimately we just gave up, and used Windows 7 Home(!) for three years.
People want to give Microsoft money, but Microsoft is intent on making the entire thing as painful as possible and their licensing as obtuse as possible. Office 365 Business gets a lot of shit, but it is a dream come true for startups, you pay one cost, and one user gets their Office license key, email, and some cloud storage taken care of.
Where is the Windows version of Office 365? Why can't I just pay a per user fee and get one Windows Enterprise key, the CAL, and Azure-based AD?
Time is money, and Microsoft likes to waste a lot of time. I'd prefer to spend a few dollars more a year and have a simple streamline process of licensing, than spend weeks being jerked around just to maybe get a few bucks off of a fake price anyway.