Um, let's not pretend creatine and anavar work in the same way.
But even assuming they work in the same way, the difference is simple, any who eats meat is already getting creatine. It's no different to protein. It's derived straight from food. Anavar is synthetic testosterone.
The only PED that is somewhat hypocritical is caffeine, which WADA has banned at various stages. Very difficult to police as it is found in so many things we consume and have formed an almost unbreakable cultural practice over hundreds of years.
It's not as if no one ever thought about what constitutes a PED. There is plenty of literature on the topic on the WADA website if you care to look.