Percussive Patterns in the Music of Mainland Southeast Asia

Since the publication of Music in Java (1949) by Jaap Kunst, the elaborate rhythmic organization of the Javanese gamelan is no longer in question, but published works on the music of mainland Southeast Asia do not indicate any of the rhythmic complexities of the gamelan and are uniformly transcribed in 2/4 or 4/4 time. Are we to assume a sharp break in the musical traditions of Indonesia and mainland Southeast Asia? Do the simple duple or quadruple meters found in the transcriptions of mainland Southeast Asian music encompass all that need be said concerning rhythmic organization? Or is there a higher level of rhythmic organization which has escaped the notice of most observers?