Word vs. WordPerfect
If you can overlook the abominable layout, this thorough description of the technical differences between the file formats of WordPerfect and Microsoft Word serves as an interesting analog to the difference between tag-soup HTML and properly applied, CSS-formatted semantic HTML.
Their current relative market shares might be considered somewhat significant. Also, note the difficulty in translating WordPerfect's proprietary printing system to the standard Windows model. I remember dealing with that particular problem with my clients around the time of the DOS-to-Windows shift, and the idiocy of having to install an application-specific printer driver for a Windows program still boggles my mind today.
Like most Microsoft competitors, it seemed like they were determined to help Microsoft win their market as quickly as possible.