Only mods see those tags.. I usually moderate out anything I see popup porn-wise as well as the competition entries. [battle!] adds the screenshot to the competition queue for judging.. not every screenshot goes through, so generally more polished / finished looking entries that aren't concept art or menu shots get entered into the showdown.
When I originally allowed all screenshots to compete it got a bit crazy with rather boring entries.. too much having to sift through them and you just lose interest. (Picture a grayish GUI shot from a configuration tool against a half-finished stick figure game) Instead, there is a level of initial moderation to pick the entries and then the community does the rest when they are compared side by side.