The open-source development model is all about choice. More and more, there is an endless number of places to grab software. Windows NT is not the only choice. With the freedom to copy, modify and distribute software, boundaries begin to fall away. This is a freedom which people, certainly businesses, are flocking to.
Cost is only a fraction of the issue.
Freedom to get what you need from the software is the main attraction. Cliff Miller has Turbolinux dominating Linux sales in China, a country that is considering adopting open-source software as a country standard. Doc asked Cliff how he thought the Chinese perceived Microsoft. Bernie Thompson theorized that the reason for this could be that the Chinese government is wary of building its IT solutions around one US company. I would add that Microsoft is capitalism in the purest of forms.