i'm actually afraid to roam the countryside because of enemies always attacking my horse. i could be standing directly in front of the enemy, power attacking his brains in, and he'll move past me in order to get at my horse. and my horse thinks it's invincible because it gets into fights with anything around it after i dismount.

i just can't figure out why Bethesda programmed the enemy AI to prioritize my horse over me, or why my horse doesn't run away. is this a common thing in skyrim?

Get an undead horse. Problem solved.

But yeah, kinda frustrating before you do that.

do i get that at the end of Dawnguard?

Well, http://www.uesp.net/wiki/Skyrim:Arvak. (Spoiler warning, obviously.)