Office for Mac is just a way for Microsoft to prevent Mac users from using formats incompatible with Office for Windows and creating pressure on Microsoft's format monopoly. It has to be usable, but must never feel better than the Windows version.
On the other hand, Office for Mac likely has <5% marketshare at most, so Microsoft could legitimately justify less development resources as making financial sense, similar to how Mozilla and Google treat Windows as the primary platform for Firefox and Chrome respectively. On the other hand, I wouldn't be surprised if the marketshare for iTunes on Windows exceeds that of iTunes users on Mac OS X, so there's really no excuse for that particular half-arsed port.