That's the only explanation I have for it.
There could be no other reason I go to forums about movies and books I like expecting intelligent discourse.
I went searching this morning for stuff about The Dark Knight teaser trailer (if you'd like to see it, it's on my journal) and I kept seeing comments bitching about how there was no footage, only dialogue.
Ok, for those of you having similar thoughts, let me explain a thing or two. Listen very carefully to this first point.
1) THEY ARE STILL FILMING THE GORRAM MOVIE!!!
Any footage they selected may or may not be used by the time the movie comes out, or may exist in a different form. Using footage in a teaser would be a stupid move on the part of the studio unless there's a shot they are absolutely committed to using.
2) Wikipedia defines a teaser trailer as: a short trailer used to advertise an upcoming movie, game or television series. Their purpose is less to tell the audience about a movie's content than simply to let them know that the movie is coming up in the near future, and to add to the hype of the upcoming release.
So basically, they're just starting the buildup to the release. You more than likely won't see a full trailer until about Christmas. But people want everything NOW. Anticipation, buildup, these aren't things folks are interested in. The mentality is increasingly becoming, "I want it, gimme!"
I am SO becoming a curmudgeon the more time I spend online.