Mucman, do you really want an answer to your supposed observation? It would seem to me that if you are as curious as you profess, you would be willing to reexamine your observations so you could understand your own question.
I should remind you that when you use the term "most", then you are admitting a qualifier there for comparisons. Hence, there is subjectivity. And as far as my observation too, heavy metal, techno and rap have the exact same tendency with loud . . . or loudest, to please you, systems. Why you keep ignoring this statement and focusing on techno and rap makes me wonder where exactly your bias is directed. I will concede that rap and techno have loud systems, but to exclude hard rock is preposterous. Sorry I cannot help you in your disingenuous attempts to uncover a supposed truth.