"If you have a shortcut to an executable, then the LNK file handler says, "Okay, this is a special case...."" But most shortcuts are shortcuts to executables (when they are not shortcuts to documents; and on those, we know that we can't edit the command line).
The shortcuts to Office applications (probably via the shell namespace objects) that would SEEM to be shortcuts to executables are strange, when they don't allow you to edit the command line. So I see the OP's confusion.