What's the difference?
I mean descriptively. I know the mechanical differences, but how do you describe, oh say, a vampire's Slam vs a vampire's Unarmed Strike?
A vampire punches you in the face. It's super-effective! Take d4+str lethal damage and suffer two negative levels!
vs.
A vampire punches you in the face. It's not very effective! Take d3+str nonlethal damage and enjoy your free attack of opportunity.
The best explanation I can imagine is that slam is less so much a strike, but more of a general smack down. Slamming someone into the the ground or walls, flinging them about, general backhands, etc. It is the kind of moves you expect from a large brute such as a gorilla, rather than a monk's precise and focused blow.
Essentially, if I had to pick an example that most people have seen.... it would be that scene in the Avengers where the Hulk treats Loki as a rag doll....Don't tell me you don't know the one; just youtube it for a refresher and tell me that wouldn't be a 'slam' attack.
No explanation about why you get negative levels when a vampire does it. I would imagine a bite attack would be far, far more natural for that. But meh.
i tend to view slam as a solid no technique punch using one or two hands. sort of like the classic swing you would see in an old movie with a mummy as the bad guy.
All of the descriptions of a "slam" I see above would also work perfectly well for an Unarmed Strike.
And Unarmed Strikes don't have to be "monk precise."
That's what's weird to me. :P
Unarmed Strikes provoke unless you have Improved Unarmed Strike. Slam attacks don't provoke (in general). Rather than give a large number of monsters IUS, they gave them slam attacks instead.