OMFG. Are you fucking kidding me? Where's Microsoft Office for Ubuntu (or any linux distro)?
You can use it through MS Office online. Why bother to create a native product for a platform that virtually nobody uses? They create a native product for Windows, OS X, iOS and Android but building native clients for Ubuntu or Solaris or FreeBSD doesn't make sense so they offer the web client. Microsoft aren't alone in doing this, companies like Adobe and Autodesk are the major players in terms of content creation applications and also target those platforms but not the minor players because it isn't worth the effort.
Minor players in the desktop market are much like Meego, Windows Phone and webOS in the mobile space, they are good operating systems but they were late to the game and don't offer any compelling, disruptive features that would entice users - and developers - to switch from the incumbents or even to expend effort to support them.