Well... in most cases, it is, I guess. xD
Like, there's Fire can burn Grass to a crisp in real life, but how can a bird (Flying) defeat a karate dude? (Fighting)
This question was previously asked on the PokeBase, and the answerer thoroughly explains why each weakness and resistance is somewhat logical. Credit to Aeternis for making the answer. :3
Hope I helped. :)
Source: Experience