Another path to Windows: Doom -> PC -> Windows
As is evident from the discussion here, there are many reasons we've ended up with windows as our default. I think there is another reason which hasn't been mentioned yet, the role of computer games and specifically the game, 'Doom' in my case, has been a huge factor in getting PC's and hence windows into our homes. Admittedly Doom was written for DOS not Windows, but Windows monopoly sprang from an existing DOS monopoly as I understand it.
In my childhood, my interest in computers was mostly due to computer games, from the old 8-bit home computers through to 16-bit computers and eventually onto the PC. At that point when the PC was already taking off in offices, as people have mentioned here, MS Word has been a big driving force in this area, the PC was rarely seen in homes unless someone worked from home maybe. My perception of the PC at that time was that it was no use at all for games. In fact there was no sound even, unless you bought a sound card, also I assumed Windows was kind of built in OS like workbench on the amiga, or BBC Basic on the BBC micro. I realised of course you had to get a copy of Windows, but i certainly wasn't aware what alternatives there were.
Of course through time PC's started becoming much more commonly seen in homes, the thing that blew me away was seeing Doom for the first time. This was when I realised that the commodore amiga had been left behind. Many others like me saw Doom as a reason to own a PC. By this time the PC was already fundamentally linked with Windows, at least from my own experience, I didn't even realise there were alternatives to Windows at that point as I already said.
In the modern marketplace games are a huge industry. What platforms are they provided for today? Er windows and... nope just windows (not counting non-pc games such as Playstation obviously). I often read newsgroups where people say they will not upgrade to linux because they can't play games or people who do use Linux often keep a windows partition for playing games. If games companies started writing games to run under Linux I believe Windows would fizzle out in the home environment, if it isn't already on the way out. I have to ask why they don't provide for linux? is it too difficult because of all the types of distros?
Today, I still use Windows, it is my default at work because it is my work's default. At home I now use Linux more than Windows, which I am very happy about. The learning curve can seem steep moving away from windows but is very worthwhile. To my eyes the innovation in open source software far surpasses the innovation seen from MS lately.