I think a slam is a very different beast than an unarmed strike. An unarmed striker has to worry about injuring himself with his own attack and uses technique to minimize the risk of self-injury or self-infliction of pain while maximizing the damage done to the enemy. A slammer doesn't have to worry about self-inflicted injury because of their supernatural composition, protection, and/or abilities.
At least, that seems like a reasonable division to me. Supernatural slammers like golems and vampires have less fear of Newton's 3rd law - they're not going to hurt themselves no matter what.
-George
Edit: It's kind of like how Thai kickboxers will kill the nerves in their shins (by repeatedly hitting a tree, I think) before a match. This opens an interesting line of martial arts feats that I haven't seen elsewhere - a power-attack like feat for unarmed strikers: Minimum STR 15, you do 1 bonus damage for every point of damage you decide to inflict on youself, up to your BAB. This bonus damage can stack with the damage from power attack... Cool!
-George