Man, some of you just bitch far too much.
Everyone has been calling it Batman vs. Superman since the initial announcement so the title pretty much being the same is not that surprising. It makes sense too from a marketing standpoint as it'll help them generate interest for the main pitch of the movie. It's not like people will go around saying the full title including the subtitle like idiots. Everyone is basically going to call it Batman vs. Superman. Also, World's Finest is a pretty crappy title too from a general standpoint. The general audience isn't going to react better to that than Batman vs. Superman. The latter title works better in that respect.
Not to mention, since when have these comic book movies had any particularly good titles outside of The Dark Knight?
Every one of them is either X-Men, or Iron Man, or Thor, or Batman Begins (this title only sounds less ridiculous now because the movie was actually good), or Avengers? Most of these titles are uninspired crap. Batman vs. Superman following that tradition isn't exactly alarming.
Seriously, the next big comic book movie is called 'Avengers: Age of Ultron'. And don't one of you bloody comic nerds actually try and argue that's somehow a good title because it's just as shitty as most of these.