As I was looking at the barbarian class in S&P I noticed it seemed really powerful compared to other traditional d20 classes. Is this to compensate for the fact that characters wont have magic items to advance in power?
Kind of but not entirely. In general, Conan classes are more powerful than standard d20 classes. However, Conan isn't intended to be compared to D&D classes - it has a different magic system, combat system etc. In addition, Conan has its own monsters/enemies so Conan characters aren't (as written) going to be encountering the range of D&D monsters that need magic to be hit.