There are many arguments for having some kind of system behind the assignation of the words. We decided to assign the words randomly as this makes error correction much easier. If similar 3 word combinations were placed near each other, it would make it much more difficult to notice a mistake. As it is, the system has been designed to have similar 3 word addresses a long way away from each other, so it is immediately obvious if a mistake has been made.
Also, there simply aren't enough words available to apply the kind of naming structure that might be associated with other address systems.