Over the years I've puzzled over the Microsoft-CAD vendor agreements (unwritten or otherwise) to not step on each other's toes. Microsoft doesn't do CAD in exchange for CAD vendors limiting their software to Windows APIs. For example, before Microsoft bought Visio, it required Visio to unload IntelliCAD, their AutoCAD clone.
I could see the benefit to Autodesk, SolidWorks, Solid Edge, Bentley Systems, et al: write their CAD software using the APIs of just one operating system to cut development and support costs. In exchange for supporting the monopolist, the CAD vendors get cost and support benefits, I am guessing, from Microsoft -- just as hardware vendors got lower-priced OS licenses in exhange for supporting the Windows monopoly.
This thing's been sitting in the back of my head for years now: what benefit does Microsoft get from CAD running only on Windows? Duh!
I finally clued in yesterday after reading a slash.dot comment from senatorpjt: "Nobody is ever going to be able to market a PC with a non-windows OS [because] (almost) everything on the market requires Windows."
Microsoft benefits from vendors locking their CAD customers to Windows-only computers. Ten million people forced to run Windows means that Microsoft earns another $1 billion (at least!) in extra revenue from OS sales, upgrades, and ancillery products sold to CAD users.
That's why there'll never be an AutoCAD or SolidWorks or MicroStation for Mac OS or Linux. So start tearing up those Architosh petitions now.