Yes, the show is airing now, but HBO is still releasing trailers. The latest Game of Thrones trailer is 30 seconds of quick cuts from the series (including a bunch we haven’t seen yet) interspersed with quotes pulled from TV critics’ reviews of the show.
Winter Is Coming: An effective little trailer. Certainly one that could entice people on the fence about the show to check it out. Since it is 30 seconds long, I’m guessing HBO will air this on broadcast and other cable networks to attract new viewers.