Andor said:
If a human NPC has the ability to brew a potion or animate a zombie or conjure a chipmunk then I want an in game explanation for why my character can't learn it. "Animating zombies is a divine gift of Orcus and you need to devote yoursef to an evil god to do so." is a valid reason why not. "Because you can only learn that at NPC vocational" school is not.
They pretty much equal the same thing.
In either case, my personal opinion would be that the PCs can learn these things, they just have to do some research into it.
If the player is willing to do research the DM should be willing to create a new power modeled after the NPC power. It's not that hard.
If it's something really bizare that could cause problems, then introduce something like the above... Where a drawback would make the power less disierable, and only the truly devoted would want it.
For most stuff I think it will be safe to just say hey that was unexpected and move on... The orc can shoot acid balls? Cool, I'll shoot it with my own acid ball!
Do you REALLY need to discover the means of exactly how an orc shoots acid? Or would you rather kill it and take its stuff?
I personally think a lot of the problem stems from the unknown.
A monster might have any power imageanable. This makes fighting that monster an unknown. The unknown is scary. Some people like being scared. Others want the player's guide from day one.