James, I can't direct you to anywhere in particular that says that, other than articles I have written personally, which you perhaps will not consider to be that useful in this particular debate - although some have been published in Thailand. Actually, I would also assume the majority of Thai judges will say all techniques can score the same. However, what is done in practice is that particular targets and techniques are favoured. The application of unwritten rules in sport is not just limited to Muay Thai, a number of sports have a set of written rules of 'unwritten rules' or normative rules.

I interviewed a number of top Thai judges, experienced Thai trainers and top Thai boxers in Thailand over a period of years as part of a PhD study. They were very consistent in their responses and if they couldn't always explain exactly what they meant, they gave clear examples in actual fights. In his post above Kevin actually quotes a referee I interviewed, Wanchai Prowsee (who was voted best referee/judge at Rajadamnern in 2003) and trains judges at the stadium), he said when considering an equally effective punch and body kick exchange, the body kick would win because "it is the logo of Muay Thai and a punch is international".

The best evidence I can suggest is to watch lots Thai fights judged in Thailand. This particular fight between Daitan and Jamal is actually a great example of the emphasis on particular weapons in scoring, but given this fight is the 'bone of contention' I realise that is a circular argument. While not quite the same, there is another example of an aggressive puncher losing a world title fight in Thailand against kick and knee, this fight also illustrates the importance of particular techniques in determining the winner (this fight was judged by top Thai officials in Thailand).

http://muaythaijudging.com/fight-1.php