I have to disagree here - you can absolutely run a large organisation on Linux (the Frenchies do it,e.g.).

The issue is the middle ground. A large company can absolutely invest into what's needed for that. They might even come out cheaper.

The small to middle companies are the issue. The ones with 1-10 people running their whole IT. For them, Linux based operations are an issue - there currently is absolutely nothing that is as "one module working well with another" than AD. (Which should please not imply that AD is well designed and working too well). Period.

I have just kicked Microsoft (mostly) out of my company. But that is my personal decision - I am the CEO and we are small enough that I can do most IT support myself or with the help of a small outside company. But boy,did that cost us time and therefore money and still there are drawbacks and things that will not work as smoothly as they did on windows. I am thankfully able to do that - as I have no external venture capital I have to answer to, have staff that is very tech literate (especially considering that none has an IT background),willing to learn and don't need software too much that requires windows. (Well,some, e.g. occasionally CAD)

But would I ever recommend that to anyone? Nope. Definitely not.

Which pains me to say.