There are programs that do not require a full path to the exe. Outlook.exe is one. Probably only MS programs, I dunno. Play around with em.
Or check the entries under "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths" in the registry.
There's plenty of non MS programs that add themselves there

To name a few:- Firefox, Nero, Winmerge, Acrord32, Winrar. To run any of these you only need to e.g
/run firefox[.exe] [parameters]Plus of course, anything in a directory in the %path% variable.