> supported until 2020 (!). There is no Linux distribution outside RHEL
The RHEL derivates such as CentOS or Scientific Linux provide such long support.
> that many existing Windows software doesn't work on Linux, compatibility of LibreOffice with Office documents, etc
There is Wine which allows to run Windows programs on Linux just fine. I am still using Office 2000. Compatibility is also problem with newer Windows and I would say that in long run Linux will be more compatible with WinXP than Windows themselfs. Microsoft seems very eager to drop old functions to boosts its sales.
You are also forgetting that upgrading Linux is usually much easier. MS is changing UI every version and it requires retraining users and administrators.
The RHEL derivates such as CentOS or Scientific Linux provide such long support.
> that many existing Windows software doesn't work on Linux, compatibility of LibreOffice with Office documents, etc
There is Wine which allows to run Windows programs on Linux just fine. I am still using Office 2000. Compatibility is also problem with newer Windows and I would say that in long run Linux will be more compatible with WinXP than Windows themselfs. Microsoft seems very eager to drop old functions to boosts its sales.
You are also forgetting that upgrading Linux is usually much easier. MS is changing UI every version and it requires retraining users and administrators.