People need Word in the same way other people need Emacs or Vim. It is their preferred tool for the job.
Then it's not a matter of "need" at all. If one is willing to give up all of the advantages Linux has over Windows so they can run a particular word processor (which IMO isn't very smart; a word processor is a word processor and there's not much difference between any of them), more power to them.
Well, we could argue that no one actually
The point I was trying to make is that even for applications with perfect compatibility (text files & Emacs/Vim) a user's preferences can be strong, and switching from one to another a rather time consuming thing. Migrating to another Office application (Word/Excel --> whichever is the OpenOffice clone) is just a lot more expensive because you don't have (whether we like it or not) perfect file conversion.
Honestly, a lot of people need Word, because in real life, you don't have any time during your work day to be figuring out conversion problems between Word and OpenOffice.
For the perspective of an end user that prefers applications X, Y and Z only present in Windows, what kind of advantage does Linux actually offers? It used to offer more stability and security, but honestly I don't see Windows 7 being sensibly behind at these.