Maybe it was a bit of exaggeration, but I think maybe you don't realize how much things have changed. In the late 90's it was difficult to avoid using a Microsoft OS. First, the commercial operating systems available were mostly niche products with relatively little software available. What was available was not compatible with what most of the world was using.
Linux was gaining popularity, but it was difficult to install and use. It lacked the quality desktop apps that are available today. It lacked a coherent and usable desktop. I think it was around 1998 or '99 that I installed RedHat 5.2. It came with fvmw2 or something. It was hideous, and that was only after I spent hours trying to configure X in the first place. There was no free MS Office-compatible word processor. StarOffice came out around then, but it was commercial and pretty lousy. It was years later that there was decent office software that was compatible with the rest of the world. Netscape 4 was pretty much the only game in town for web browsing. Fonts looked like total crap. Oh, and that's if you could even get your modem to work in the first place. Winmodems were everywhere. I went out and bought an external 56k modem for like $75 and spent weeks getting it to work. I could go on, but I really don't like thinking about the bad old days.
Basically, you were stuck with Microsoft back then. They may have only lost %5 market share or some small number, but there are very good alternatives available. Market share hardly matters at this point for end users. Whether you choose MS, Mac or Linux you can expect wide support.
It's a very different landscape for end users, as well as Microsoft.