In the world of web servers, Microsoft isn't much of a player. In that respect,
I'm not wrong. However since most businesses are under the marketed impression they need Microsoft Exchange to be productive, Microsoft has a pretty good foothold.
I'm not trying to spread anti-Microsoft propaganda, I got sick of that back in the late 90's well before our current Apple vs The World state of affairs. I'm just stating that while they have a very solid business model in place that has put them into a lot of homes and a lot of businesses, they do not command a monopoly.
They do command a ridiculous amount of power, and have raised the barrier to entry far beyond what it was early on in the game, but they haven't closed the doors by any means. The underdogs with the backing to compete have in many markets started to surpass Microsoft. In some markets, such as mobile, they're the only reason Microsoft is making money at all (patent trolling is fun for the whole family).