Pink Floyd kind of got their first flush of success doing gigs with an innovative light show created by their landlord, who was a lecturer at Hornsey Art College. In the '70s they started projecting films behind the band as they played. Three of their eight pre-Dark Side albums (including Zabriskie Point here) were soundtracks. Us and Them started off as a piece for the Zabriskie Point soundtrack, where I believe it was supposed to be used as kind of ironic counterpoint to footage of riots.

So in a way it's not too surprising their music makes a good soundtrack. They (well mostly Roger) always had the full audiovisual experience in mind.

Edit: The instrumental section of Money is based on the live soundtrack they did for the moon landing in 1969.