There is a discussion over on the Futaba support forum regarding channel assignments. The 72 MHz PCM G3 offered channel grouping so that groups of channels would all update at the same instant, vs. each one responding as its position in the serialized data stream arrived.

There has also been speculation that they did some clever things about more frequent updates to the least significant bits in the digital PCM words, and less-frequent updates to the most significant bits. This allowed fast response even with 12+2 channels, with the limited frame rates imposed by the 72 MHz carrier frequency.

2.4 GHz systems can have much faster frame rates, and the advice I saw Bax give for the 2.4 Receivers was not to worry about channel grouping or channel assignments.

Dave