My future wife had one of the early "IBM Compatible" PCs and I liked some of the programs one could use, like Quicken, Prodigy (an information dial-up service), good spreadsheets and word processing. My home computer has always been a DOS/Windows machine since.
Windows had good calendar and email programs long before they were available for Unix so at one point I got a PC card for the Sun in my office which ran Microsoft Windows in an Unix window. As I found myself spending more and more time in that window, my next machine was a Windows machine with an X-Windows program so I could connect to the department's Unix machines to use Emacs and LaTex.
Soon very good Emacs and LaTex programs became available for Windows and when I moved to NEC in 1999 I went Unix free and haven't looked back. My biggest complaint about Unix was the user interface. To print pages 3 to 5 of a latex document is easy in windows, for Unix I had to do a man dvips since I could never keep straight which flags did what. Once I spent hours trying to figure out what I did wrong in a Make program (I had uses spaces instead of tabs). I'll never forget the time I accidentally typed "rm temp *" instead of "rm temp*".
Ever since people have kept telling me Linux interfaces and programs have gotten much better, and they have, but never enough to get me to switch back. Some Apple lovers have tried to get me to move to Apples, but they just never had the software available that PCs do. Windows emulators for Apples are popular but you don't see the need for the other direction.
As more and more of the programs I use become web based, the actual platform becomes less and less important. Still though as someone who likes an easy user interface and wide availability of programs and doesn't do much programming and scripting, Windows has worked well for me.