The Keeper wrote:
We always sit though the credits anyway so if they wanna tack some tidbit of a clue to the next one onto the end of STID I ain't going to complain. Usually we're the only ones left in the theater by credits end unless the general public knows there is something to see.
Exactly. The post-credits "bonus scene" is almost always intended for those who know it's there going into the movie (i.e. the diehard fans). So, once the credits are done, having a obscure shot of the Botany Bay being discovered would be akin to what was seen in Avengers.
Claiming it's the same as the scene at the end of the Dark Knight, however, is wrong. First, that was pre-credits, so everyone saw it. Secondly, EVERYONE knows the Joker is the arch-enemy of Batman, and EVERYONE was expecting it (probably most had no clue who/what the League of Shadows was, actually). You can't make the same comparison with Khan and Kirk.