Wikileaks has leaked all sorts of interesting documents like scandals related to the economic collapse of Iceland etc. It's just that this current affair is of such a magnitude that it overshadows all other leaks.

It's also a matter of global interest. If these where cables leaked by Belgians written in German they wouldn't have received the same attention because no one really cares about Belgium, and Belgium certainly has little to offer on the matter of global politics that could be of interest and have implications for all other western nations.