Mechanically what are the differences between draft and riding horses? Is it impossible to ride a draft horse or can you just slap a riding saddle on one and ride it. In addition is a riding saddle actually required? Plenty of people ride bareback especially for short distances?
A draft horse can be ridden, but war horses get +2 morale and an extra hoof attack (per the Horse entry in the Monsters chapter).
While true, draft, riding, and war horses are three different categories (at least in the case of medium horses, the only horse type that has all three on the table at different costs).
I am not aware of any specific rule that forbids riding a draft horse. I personally would certainly assess some kind of penalty for someone riding a draft horse. The same is true of someone riding bareback.
I’m sure both of these things are possible, but they’re more difficult than riding a horse that knows what it’s doing or using a saddle.
Draft horses are horses that have not been trained as mounts. Not every animal can be trained in the role its trainer would wish because of the random factor of how many tricks an animal can learn.
This is elaborated upon in the 2015-upcoming Lairs & Encounters. Here is a brief excerpt.
Mounts (M): Mounts are trained to carry a rider on its back and accept his directions. Mounts will not wear barding, and will not charge into melee unless natural predators. They will not attack with their natural weapons while carrying a rider. A proficient character (one with Adventuring, Animal Training, Beast Friendship, or Riding proficiency) can safely control a ridden mount outside of battle. If the character has Riding proficiency, he can control a ridden mount in battle; and outside of battle, he can control up to six mounts, one ridden and the others ponied on lead ropes. An unproficient character can safely control a mount on a lead rope, but cannot ride one without grave risk to himself (save versus Paralyzation each round or fall off). Mount training counts as five tricks, so when dealing with less-intelligent beasts, suitable specimens might be rare and expensive. Note that even sapient creatures which are to carry riders must be trained as mounts, because the subtleties of communication between rider and mount, and of movement while laden with a rider, do not come naturally.
War Mounts (WM): War mounts are trained to carry a rider into battle and accept his directions despite the chaos around it. War mounts will wear barding, and will charge into melee, even not naturally willing to do so. In melee, war mounts will attack their masters’ targets using their natural weapons. War mounts are subject to the same limits on control as mounts (see above). As with guard training, war mount training increases a creature’s morale score by 2, to a maximum of +2, and war mounts without riders can function as guard creatures. Training as a war mount is even more demanding than guard or mount training, counting as eight tricks. Very few animals have the intelligence and temperament to serve as war mounts, so they tend to be very expensive. Sapient creatures which are to carry troops into battle must receive war mount training. Unlike creatures of animal intelligence, their morale score is not increased by war mount training, however.
Workbeast (WB): Workbeasts are trained to pull heavy loads or carry burdens. Workbeasts are not trained to accept a rider, and in battle or other stressful situations will tend to react according to their natural instincts (fleeing if a prey animal, or attacking if a predator). Teaching an animal to be a workbeast counts as two tricks. A proficient character can safely control six workbeasts, and an unproficient character can control only one.
Do tell …