Yeah, there is a bit of a difference between sending a message, and giving the show away.

Such as an anakin themed trailer might suggest the potential for emotional turmoil, without revealing that he turns to the darkside etc. Its about introducing the threads of a story. A teaser trailer however is much more abstract, its either throwing people off the threads, or just introducing an abstract concept.

The Dark Knight Rises trailer for instance plays on defeat and.. well... rising. The original Dark Knight Rises teaser introduced the idea that it would reference Batman's past with the league of shadows. The earlier Dark Knight teasers were literally just 'look its the joker!'.