I bet it is true. A prologue is an introduction scene in a novel that usually doesn't seem to have anything to do with the rest of the story and may introduce a character or a scene which isn't relevant until later in the book. In my opinion, a lot of writers use a prologue to info-dump the reader. (Trust me, I'm not immune - I'm cutting the info-dump of a prologue from my current project.) Most readers will skip a prologue. If they were intrigued by the back cover of a book, they don't want anything that will ruin the story for them later on. A prologue might enhance the story, if the readers cares to read it, but it shouldn't be vital to the plot. The first chapter is what should be extremely important. Prologues can be used for dramatic effect, such as getting the point-of-view of the bad guy in a crime novel. Those sometimes work well.
Ah, but what about prologues in movies? Those aren't terrible.
Prologues in movies are usually more accepted. With a book, the reader can get a sense of the world by reading the back-story as it is spread throughout the story. That can be harder to do with a movie, though I can think of two examples of prologues that are my favorite. Some movies will start with a prologue that explains some of the timeline, such as "National Treasure" where the grandfather explains to the boy about the history of the treasure. It fits.
Here is an example of two prologues that work very well: (My favorites!)
(Sorry about the subtitles, it was the only one I could find. I love this! It gives us a great background, letting the audience see a map of Middle Earth and it's got some wonderful lines!)
I think a book can have a beneficial prologue, but if the information is so very important to the plot, it can probably be written into the story in a nice way. Honestly, I will probably skip a prologue and just start reading the story.
Can you think of a book/movie where the prologue worked or didn't work?