EyeShotFirst said:

I still don't believe it's as simple as all that. I think the basic ingredients of the Chuck Berry, Elvis, and Buddy Holly "Rock 'N' Roll" are still very much a part of the AC/DC, Led Zeppelin, and Van Halen "Rock".

To a greater and then a lesser extent.

Jimmy Page was playing Blues-Rock in the Yardbirds, it wasn't until Led Zep that it became what we now look back on and call "Classic Rock". Similarly The Who were a Mod band (Who had a mid career dabble with the psychedelia fad) before also finding that "Classic Rock" sound with 'Live at Leeds' and 'Who's Next'.