Fair point - but that is a legacy. In any case, my question was poorly phrased (for which I apologize); have army books had the option to put a character on a montrous mount which is found in the rank-and-file unit entries? That is, is there an option to put a character in a unit of monstrous cavalry mounted on the same sort of animal, or is it a fudge?
Personally, I would LOVE to see characters on MC and I don't think it would be too difficult to work it out - use the highest of the two W characteristics? How does it work for Pegasus? BUT it might end up being expensive to fit a character on there if the W bonus is lesser. There was a discussion thread that a Demigryph would be worth about 55pts to a character - you could get a whole other DGK for a little more, right?