Once again, note the difference between just any charge - you can charge people while wielding a saber, because you get some decent shock effect anyway - and specifically the couched lance charge, which is what would supposedly use the steed's damage bonus.
The weird thing about mounted combat in RQ is that you get no bonus from just being on horseback in a fight (barring mounted archery, which is excellent), or from a charge outside of the lance effect. Once again, Pendragon does this a lot better.