Tricks on anime trailers..  

I know what you mean. I've noticed that too. That really reminds me of the trailer for that third Bleach movie. They made the trailer look so cool with all that fighting and everything but when I actually got around to watching it it was a downer. All the excitement from the trailer led to a mediocre story. I do get the point you're saying with the action-packed scenes too. I think it's done in a lot of trailers and not just for anime shows. They'd show some really awesome scene but when you get around to watching the movie that particular scene just flies by really fast or something. Takes the excitement out of it.

Trailers are just there to show what is currently in the works. It's all pending stuff so you still don't know what will come out in the final product. All they're used for in my opinion is to show that the anime you liked is getting a shorter version with minor improvements over the original show.

Yes, you're not supposed to expect everything that appears in trailers, these kinds of things happen when producers are trying to raise their popularity before the final product is out. The problem is that there will usually be last-minute changes on every project, but most of these aren't seen in the trailers so people tend to not notice.