One of the great virtues of these illustrations is that they expose flaws in the verbal statement of what we are trying to convey. For example, it is not a good idea to state 3.1 before 3.2. In the rough draft illustrations, the illustrations of 3.1 and 3.2 leave the reader free to believe that they are not easy to do at the same time. Unnecessary differences between the layout designs in the 3.1 illustration and 3.2 illustration confuse the reader because they must then construct in their mind a different example that illustrates both 3.1 and 3.2 at once, in order to believe that they can follow this set of guidelines. We don't want to leave that exercise to the reader.
People react to illustrations in a gestalt way.
Trying to illustrate one principle with an illustration that violates another principle or even clashes with another illustration will risk delivering the message that the different rules cannot be satisfied concurrently and the reader may ignore our advice because they can imagine it is impossible to comply. The way this problem has been solved in the past is that while the book introduces features and examples of these features first, followed by a comprehensive example that combines the features, the authors of the book have to develop the comprehensive example first and then extract the feature examples from the composite to use as the feature illustrations. So navigation blocks play a particular role relative to the site. They should be presented consistently to theme this relationship to the site, regardless of what frame, table or page they happen to be part of. Avoid differences in presentation qualities that lack a compelling motivation based on 1. and 2. above.