The dominant OS for Business (on desktops) is Windows. This can't change (soon), too many companies are locked into software that requires it (either built in house or purchased).
That's changing, more applications are going web based. But there are always those little niche apps that hang out in purchasing or accounting that require windows and aren't going away soon.
Most companies can't function without Excel. Go to the accounting department. Even if they have an "accounting system" ask the people working their what the use (or watch them). They probably have Excel open all day. Excel is hard to do in a browser.
Every company in the world would love to be MSFT. High profits and a locked in customer base.