Actually there is a reason to skill this if you plan to use Horses/Stallions/Mooses/Courier Horses:
The skill caps the effective quality of the horse and therefore the speed of the horse.
If you ride a q10 horse with 30 skill, it has the speed of a q10 horse.
If you ride a q60 horse with 10 skill, it has the speed of a q10 horse (skills caps it).
If you ride a q60 horse with 60 skill, it has the full speed of the q60.
It gets more interesting with higher quality courier horses.
BUT if you want to use a warhorse, you need to do the same with the associated skill (warhorse = Cavalry, hardy and spirited = knight, heavy and royal = lancer).