Simply
I have read through the entire column of responses. Some good some bad, but I believe it is simply this.
MS Windows was the first OS marketed efficiently to the masses.
It became the de facto desktop OS and therefore will remain so until beaten. To be beat Windows, Linux has to be able to replace the core services in businesses EASILY. MS Exchange and proprietary applications continue to rule. The main decision makers for accounting and sales are not easily swayed to half-ass replacements that may or may not move their data 100%. To win, Linux has to get everyone on board. This means convincing current app builders to build for linux not just try to create a free open source one to replace them. Linux needs a single standard with one marketing vessel. Now tell me if you see that happening anytime soon.
Tell me how long it will take Windows to compete in the server market where it isn't so dominate? Once they can get past the security implications they can compete.
Linux vs Windows is an interesting ride. Windows however, has the upper hand and it looks to me like it will continue to have it unless the linux community can combine to something solid.
I could go on for ever with this. I'll what for responses, though.
Finally, personally I have no preference on Windows vs Linux, I use what works best for my clients and as of now, 95%+ are MS shops.