It is based on the approvers' opinions, but consider what they needed to do to become approvers in the first place. To reach Approver rank, you need to have proven you can consistently upload high-quality artwork. They have their position because they have shown they can be trusted to know the difference between good and bad art, as well as what is on-topic for this site. Beyond that, they can make any decision they want about what gets accepted. However, they do not need to reach a consensus. It only takes one approver to decide a post is good enough for it to be accepted.
Some posts only get looked at by a few approvers before exiting the modqueue. If that happens and you're confident in the quality, you can try appealing it. But be warned that 3D porn is not the easiest thing to get approved here.
