Legal documents are similar to computer programs in that they must be very precise and follow strict rules of construction. The comments in a program's source code would not suffice as instructions to a computer, and neither would an annotation to a legal document suffice for the document itself.
Except, of course, that legal documents are not nearly as precise as programming languages. And most legal documents have a lot of dead code--nobody really knows or cares if that code path is followed anymore. You don't want to be the guy removing sections from a legal document.
