The last thing we need is have (realistic) access to about half of the horses in cRPG. It would be ridiculous to assume that, in addition to fast, bundle of sticksy horses, we would also get access to their more manly, heavily armored, but slow counter parts.
When I speak of "access", I'm not implying that its imposssible to use the less-than-pussy horses. It is possible, but painful, given the lavish expenses and little reward.