You can pretty much develop software for Windows on other platforms too. Cross compilation is supported in several languages, and when you can't - you can usually compile stuff under Wine, or even ReactOS. So while obviously you need a computer, you don't strictly need Windows.

In theory one could do Windows dev on hard mode (on Linux/Mac): get one of the Windows virtual machines that Microsoft provides to test for old IE compatibility (https://developer.microsoft.com/en-us/microsoft-edge/tools/v...), install the freely available compilers (or even the open source Cygwin one), and code away!

I wasn't clear enough. I meant I'm forced to buy a Mac to develop for iPhone.