I think it will. Joss Whedon hates spoilers, so I think he made sure that there will be no spoilers in his trailer.

Plus, if you show the action sequences, more people will show up for the action, which means more money for the people who financed the movie.

The absolute best part was Wash going: "Oh, God, Oh, God, we're going to die." Tell me you didn't smile a little.