Blade Runner is preserved in the USA National Film Registry

-Blade Runner was selected for preservation in the United States National Film Registry by the Library of Congress as being "culturally, historically, or aesthetically significant".-

http://en.wikipedia.org/wiki/Blade_Runner

What it means that kind of preservation?

It means that a digital copy on super durable medium has been sealed in an underground fallout shelter, so the aliens who come to Earth after the humanity will be wiped out in a global thermonuclear conflict, can find Blade Runner and other great movies in this safe vault, perfectly intact.

Or something like that.

lol i asked because movies like http://en.wikipedia.org/wiki/American_Graffiti or http://en.wikipedia.org/wiki/Animal_house with belushi have received the same treatment just like blade runner from the government, but these movies are silly like American Pie or kind of so...

Not quite.

Blade Runner was accepted for the Library Of Congress already in 1993. It was one of the first films of the 1980's to be selected. Scott's Alien (1979) had to wait until 2002 before it too was selected.