Recorded songs are products, like any other product. Promotion and advertising helps sell them. Radio airplay helps recording artists sell songs. Being included on the movie or TV show soundtrack also helps. Getting the last 5 minutes of Fallon or Letterman helps. Being the musical guest on SNL helps. But radio stations, especially radio stations playing genres of music defined by sound instead of by recording/release date, enjoy a mutual benefit from being able to air music that listeners like. It helps the artists and it helps the stations.
It took some time for "classic" rock to become "classic", just as it took time for classical music to become classic. However, once the parameters of what makes a piece of symphonic music "classical" are defined, then any skilled, talented composer can write brand new "classic" music which even highly trained musicologists will recognize as being "classical music", even if only a few months old. The soundtrack music John Williams wrote for the movie Star Wars is just as much bona-fide "classical" music as anything Wagner, Bach, or Beethoven wrote. (I would have also included Tschaikovsky, but I wasn't sure I could spell it.)
European bands like Within Temptation, Nightwish, Epica, and many, many others are writing and recording brand new, classic rock in the "Progressive Rock" sub-genre every bit as "classic" as anything by Pink Floyd, The Moody Blues, or Renaissance. Grace Potter and the Nocturnals are writing and recording classic rock in the blues-rock subgenre every bit as "classic" as Big Brother and the Holding Company.
The suits who automatically present a knee-jerk defense of the radio industry might point out isolated examples of bands who struck it rich, and who owe a portion of their success to radio airplay. The truth is, there are hundreds of other recording acts, bands and solo performers alike, that the music industry chews up and spits out after milking them for all they can. Radio people usually don't like to admit that they are a component of the music industry. They like to pretend that they're something different, and that the record labels are the real villains. The truth is that the record labels and radio industry are two cogs in the same machine.