In addition, the other two decades were far more traditional and nostalgic. The 70s commercial used images from as far back as the 1920s, like Charlie Chaplin, and that would appeal to a much older audience, people that would remember the old silent films, or appreciate them. The 80s commercial was traditional and nostalgic, as well. It used young people, (as all their commercials do), but it also seemed to appeal to an older, more mature audience, that would appreciate the theme of "old friends," coming home, and being a family that the commercial implied. The 90s commercial was not nostalgic at all; it was trying to be hip, modern, and certainly appeal to a younger, hipper crowd by using big celebrities that would appeal to young people.

These commercials say a lot about society, and how it has changed, and how marketing has become much more centered on youth and young people. Before, there were old and young people alike in the commercials, and they had a "family" or traditional...

The older commercials seem kind of old-fashioned now, but they represented a different time in society, when the Vietnam War was ending, hippies were an element, and there was uncertainty about the economy, gas prices, and the government. Maybe advertisers will go back to those traditional types of commercials, now that the country is experiencing many of those same problems today.
References

Christmas 1975." Coke Commercial. RetroJunk.com. 1975. 14 Feb. 2009. http://www.retrojunk.com/details_commercial/977/

Old Friend." Coke Commercial. RetroJunk.com. 1980s. 14 Feb. 2009. http://www.retrojunk.com/details_commercial/8893/.

Paula Abdul & Elton John." Diet Coke Commercial. RetroJunk.com. 1990s. 14 Feb. 2009. http://www.retrojunk.com/details_commercial/9268/.