Answer-
1.Most of them have very sophisticated editing tools and background scripting languages .
2.Most will allow run -time versions to be distributed without the need for any 3rd parties to have the full versions of the software they were created in.
3.Due to their long history of development there is a substantial amount of supporting material and publications to help a prospective author.
4.The author tends to have the control over the data,restricting its ditribution ,as well as end users ability to alter or change material.