I have to say that as a Chilean I'm very surprised. Leaving aside my personal view of what happened in that day and my opinions on the Military Junta, it really surprises me that this traumatic event of our history seems to be very famous around the world.
I was talking about this with some of my classmates, and you can still see a lot of inherited resentment even if we we all born five or six years after Pinochet left government and 22-23 years after the coup. There many of us that want to leave the past behind, and many of us who wish to never forget, but no one here can honestly say that they don't care about what happened.
For those things and more, with date has good reasons to be one of the most important and relevant events in Chilean history, and my words may strike as odd (some might say that partisanship and naivety is to blame, I disagree with that), but many of my classmates, many friends, and myself feel the need to ask: Why is it such a known event across the world?
Two things: it's less the coup itself and more the trend of American foreign policy that it represents, and that the fact that it occurs on the same day as 9/11/01 makes it a great counter to the circlejerking that anyone in America has to live with today (though that's much less bad than it was a few years ago).
