Not all the #Arabic characters are available on the advanced toolbar. In order to scratch the itch of missing characters, Amir added "Arabic extended" characters. As you can see, even for him there are characters missing from the fonts he is using.
At the WMF we are working on implementing WebFonts; this will allow us to provide everyone with fonts that do include all the Arabic characters. When a widely used script like the Arabic one is incomplete, you can deduce how relevant it is to provide fonts for scripts that are not as popular.
Clearly, supporting scripts is necessary when we are to share the sum of all knowledge with all the people on this planet.