http://www.gamesradar.com/63-amazing-things-we-saw-and-did-skyrim/

"We had the horse shot out from under us. Enemies will always attack your steed first before they start attacking you. Once your horse is down... you ain't goin' nowhere, son."

Tell me theres mounted combat..... wow

So I have to run away in order to save my horse than put up with a fight on horseback?

You'll have to dismount first.

I'm going to ask for a mod that allows us to ride children...as they are apparently immortal.

Seriously, if we can't attack from our horses, our horses shouldn't be able to be attacked. It's not a perfect solution, but apparently mounted combat is too hard for Beth to do.

Welcome to the wonderful, controversial and ironic world of Nirn my friend.

Unfortunately yes, you have to dismount. Alternative you can try to ride pass quickly. If you can't do that, it means the place is better transversed on foot anyway.

This Idea has been presented countless of time, and presented nicely every time. But to no avail.
Mods will still be disappointing. To me personally, element as crucial as this has to come out officially.

There is no mounted combat because having a horse with huge amount of health as your meatshield would be op, even more when smaller creatures cant attack you when your riding the horse and killing them. It's for the balance of the game.

It always annoyed me in Oblivion when things would go after my horse, even after I directly engaged them in combat, and fighting multiple enemies at once made it particularly irritating. Generally speaking, I think all enemies should prefer to target the human player over their horse (exceptions being made for things like the player is running away and not actively engaging, but the horse is still close to them). If enemies are going to like attacking our horses even when we're nearby - especially if it happens even when we're directly involved in the combat - maybe we should ask for some horse armor? :angel:

'Course, according to the link in the OP, it sounds more like they attacked the horse while he was still on it, which I think is fine (though some form of mounted combat would indeed be neato). I think the real problem arises when enemies want to keep attacking the horse after you've dismounted and started damaging them.