So let me get this straight, and please correct me if I'm wrong, but abilities that cost purely mana will work and no others. Is that correct?
Pithing Needle refers to Mana Abilities. You're making a (normal) confusion between a Mana Ability and an Activated Ability that only costs mana.
Mana Abilities are abilities that:
1) Don't target anything
2) Could add mana to a player's mana pool when it resolves
3) Isn't a loyalty ability (i.e. {Koth of the Hammer}.
That's the definition of a Mana ability. Think {Llanowar Elves} or {Elvish Mystic}. They simply add mana and do nothing else, so they wont be stopped by Pithing Needle.
Any other ability with a cost (a Mana Cost, Tapping, Sacrificing, etc., followed by a Colon) is a normal activated ability that WILL be stopped by the Needle. Also, note, that while the abilities of {Deathrite Shaman} and {Arbor Elf} are often treated as Mana Abilities, they aren't. So the Needle will shut them down.
Mana abilities do not use the stack. They just add mana to your mana pool in the same way as a basic land becoming tapped adds mana to your mana pool. Which is why Arbor elf and deathrite shamans abilities are not mana abilities, like Remillo said.