Not users. What would the ability to run IE9 add to the Linux or Mac desktop? Another web browser? Do we really need one?
Not Microsoft, who would have to invest massive amounts of effort into porting it, and large parts of the Windows codebase too.
Honestly, I wonder if the author of this article was deliberately trying to think of something to criticise about IE9, and this was the best he could do.
For non-web developers who use non-Windows operating systems, IE9 is an irrelevance. For web developers who use any operating system, IE9 has to be a good thing, because it means more browsers out there that are closer to the standards.