Err, can anyone prove that (lack of) airworthiness caused the Mull crash? Thought not.
The argument we (and I was part of it) presented about the Mull was that it couldn't be proved that John and Rick were grossly negligent. From that tortuous battle it was demonstrated that the aircraft was not airworthy and there should have been some very important lessons learnt. However, we should be careful not to assert that airworthiness issues directly, or indeed indirectly, caused the crash.
Nimrod is a different story.