Even the spelling checker runs in a fairly large number, perhaps not 50 languages but close enough...
The reason the OS is so important is that everything else hinges on it.
If Microsoft has a neat application, then they should port it to Linux to see what that does to the their OS market share :) hint -- it will drop since normal folks (as M$ fans are always quick to point out) don't really care what runs under the hood. If they can get a good application to run on a free OS, great. Of course they care that is costs $100 dollars to get the latest version...or that installing the latest version might immediately make obsolete all the software titles they've been painstakingly accumulating for the past 5 years...