One of my designs (an innocent parody of the Apple logo) was rejected by Amazon. Being aware that this design might lead to copyright issues, I did some research first before creating it and found plenty of MBA designs that contain and make fun of the Apple logo (e.g. this one). Also, while I did include the word 'apple' in my description (a common English term that cannot be copyright protected), I made sure that my title and description do not violate the Amazon content policy.
When my shirt was rejected, I made Amazon aware of the design I mentioned above and asked them why they would allow this design but not mine. After nearly 2 months, I'm still waiting for an answer while the competitor's design is still up.
As a seller, I find such inconsistency in enforcing content policies annoying and frustrating. A level playing field would not only be fairer, but also make it easier to gauge which designs would or would not be acceptable to Amazon. As it stands, what choice do sellers have but to keep testing the water - which of course means extra work for the (apparently) already struggling Amazon reviewing team.