I don't like the idea of penalizing people for violating the principle of the rules. The entire point behind actually writing down the rules is so you can look at them, see what they say, and then follow them. If you want the principle to be enforced, then write it down in the rule book as "the rule."
The idea of penalizing people for violating an idea even though they are within the letter of the law just seems flawed to me. It reaks of elitism and tyranny as the "principle of the law" is allowed to be interpreted by those in power in whatever manner they choose. Unwritten rules being applied unevenly is one of the reasons that people left Europe to colonize this country in the first place...which kind of makes it no surprise that this is how European/International rules are applied.
If they didn't want the bodywork to be working in tandem with the diffuser, then it would have taken 5 minutes to write a line about the diffuser having to be a completely separate element with a divider between it and any other part of the car on the top and sides.