Yes, technical merit is important, but it is not the most important factor for most software
In every case you mention, I think you'll find the deciding factor was support. DOS won because it ran on any shitty generic PC clone. Windows won because of software support. Office won due to platform support for integration with other MS products. X86 won due to software support. ISA won due to industry support from multiple vendors. DirectX "won" (well, not really OpenGL is still alive and well for non-windows platforms and killing it in mobile with ES) due to MS platform and developer support.
Something to note for those in the Linux community who decide to flame people who are just trying to get their shit to work. Support will make or break your product, especially for business. It can have the shiniest bells and most aurally seductive whistles known to man, but if Bob at Initech can't call on someone when it breaks and actually get help, rather than insults, then it will not fly.
Even worse when the developers are actively hostile to particular classes of user (looking at you, Firefox).