The U.S. version on the DVD or Blu-ray is not the true U.S. version because it still retains the "Science Fiction Double Feature" reprise and the instrumental during the end credits. As stated above, those are not included in the U.S. version, as released for midnight showings in 1976.
When Rocky Horror had its original U.S. release in 1975, the theatrical version was the U.K. release of the film. But when Rocky Horror didn't do as great as 20th Century Fox thought it would, the film was taken out of circulation for a short period. During that time, Fox removed the song "Super Heroes", "Science Fiction Double Feature Reprise" (both deemed too downbeat), and the instrumental during the end credits, and replaced the end credits with a shortened version of "The Time Warp" (presented as the 'alternative credit ending' on the 2 disc DVD and 35th anniversary edition on Blu-ray). Fox then re-released the slightly edited film for midnight showings, starting in 1976, as the U.S. version of the film, and the original U.K. version of the film became known as "The European Version". Fox did allow theatres to show the European Version under special circumstances, such as Halloween showings or theatre anniversaries of the Midnight Shows, and the rarely seen European Version usually was a big event at those theatres.But as anybody in the film world knows, film prints get damaged due to age, repeated showings, and film breakage. When Fox allowed Rocky Horror to be released on VHS around the late 80's, they made a new master print from the negative of the original U.K. version for video purposes. But as damaged film prints came in, a replacement print was sent out, of the U.K. version. After a while, prints of the U.K. version began to outnumber prints of the U.S. version until a point in time when Fox declared the U.K. version was the official release version for the U.S..