I worked at a video store in the late 1990s. For some reason back then, it was all the rage for movie trailer voice overs to include the suffix: "only in theatres."
I think that was probably a response to piracy -- a way of saying "This movie is only supposed
to be in theaters right now, so if you see it offered on home video, then someone's trying to sell you something illegal." I still see that disclaimer in the current day.
I always thought that was to encourage those damned home video renter cheapskates to go spend the money to see movies in the theater.