[thaumasiotes]

> Well the real issue is that we're using N instead of A and D. It is A X (D X D / 2).

No, it isn't. It's AxD, where A and D are always equal. There is no reason to add another dimension to the result table when the defense or offense might pick up another type. The expanded table will never contain any more information than the two-dimensional table already does.

(Dividing by 2 isn't correct either, even from your perspective; you're forgetting about the table's diagonal. In the "space is no object" approach you're advocating, the diagonals need to be filled by special-casing, since they represent a phenomenon that doesn't exist (a Pokemon which bears multiple instances of the same type) and obscure a phenomenon that does exist (a Pokemon which bears fewer types than the maximum possible number).)