The pendants are included with the trophy. If you look at the collectables list in the main menu, included are the Artifacts, Pendants, Training Manuals, and Comics. Also, I got the "Scavenger" trophy after picking up my 28th pendant, nothing else, and there are 30 all together.
This isn't the only trophy that I have encountered peculiarities with. After completing my Survivor playthrough, and watching the entirety of the credits, the game did not give me the trophy. I had to replay the last part of the game again for it to finally register.
Don't get me wrong though-- these are very small problems. They don't really take away from my total enjoyment of the game. I absolutely love the game. I just find these things odd.