An exception clause can effect a view-shift as a means to create contrast in order to crystallize a point.
Into statements designed to emphasize total prohibition of a certain action, an exception clause may be interjected that points to some related action that is allowable as a means to create contrast between the two situations, thereby emphasizing how totally prohibited the action is, which is the main focus of the statement.
The exception clause found in Matthew 5:32 and 19:9 is not the main focus of those statements. The exception clause serves rather to provide comparison between what is and what is not allowed in a manner that causes the prohibition of divorce to be more clearly visible.
When there is more than one way of doing something, (one way that is wrong and another way that is right), and a statement is being made that focuses on prohibiting that way which is wrong, then the allowable right way may be made reference to in an exception clause as a means to bring into perspective that wrong way which is being prohibited.
So much for the claim that the exception clause could not have "jumped" to a closely associated aspect of that which Jesus was directly addressing.