It would be interesting to understand how some of these work under the covers. The reason is that they may directly/indirectly designed to work with other system tools. The obvious ones are of course e-mail (outlook/outlook express/windows mail, depending on platform, xp/vista) and browser (things changed between i.e. 6 and i.e. 7 on what was going to be allowed). To add insult to injury the platform (x32 vs. x64) also plays a part in that the command may call an x32 executable that is not mirrored from an x64 one (telnet is a good example and why I moved to a standalone SSH module).
al