In "Fahrenheit 451" dystopia has changed in the particulars of its expression, but retained certain core ideas that still speak to us. Why is...

All good stories contain themes that are relevant and relatable to people.  If we can't relate or be tied to a story in some way, it is hard to get involved and enjoy the telling of the story, whether it is a dystopian story, or a regualr fiction tale.  And, it doesn't matter how you wrap up a story--in new-fangled dystopian techniques, old-school dystopian techniques, or even normal literature; it is the core themes that drive the story, and make them interesting and applicable.

War is one theme that will always be something that people to relate to; rarely has there been a generation that has not been impacted by war in one way or another.  And, we always fear it.  And, nations are always on the brink of it.  So, war is a theme that, if in a novel, will nefinitely hit a spot with readers.  Injustice is another big theme of dystopian novels, because they are often aimed at large powers that are not just, and are cruel and suppressing.  Dystopian literature tends to take a stab at big government, tyranny, and cruelty in ruling forces.  Throughout the history of mankind, that has largely been the situation that people have had to live through.  Only recently, and in America and a few other places, has a government been less restrictive and unjust; although, Bradbury and others see trends that lead towards tyranny and fear, which is why the address them.  We all fear having our freedoms taken away by force--we can relate to that.  The repression of knowledge and learning are also big core themes because the main way that powers control others is through the filtering and controlling of information.  We are all suspicious of news sources and their motives, and have seen how propaganda and media control have worked in Nazi Germany and Communist China and Russia.  We know thse things, and so are sensitive to them.

Anything that threatens freedom, individuality, and happiness are themes that will always be important to readers, so those core issues are a safe bet when writing literature of any type. I hope that those thoughts helped; good luck!