Just my two cents real quickly...

The cavalry charges in Rome and the cavalry charges in MTW2 are, as far as I see, different things. The difference is that in MTW2 we have cavalry with lances, and I don't remember any such thing in Rome. Since one needs to get enough distance between the target and the enemy unit to actually build up speed and lower lances, just "reverting back to Rome" would probably seriously damage game mechanics.