Pedantic Point: Radio Guy, it certainly is true that many rock and roll and blues tunes were "homogenized" to make them more palatable to a wider market (or at least to the executives at the record companies), but from the early days of the recording industry on, it was common practice for labels to have their artists "cover" what ever music had become popular, in the theatre, music halls, and from sheet music, and later, the movies.

This was still true in the 50's, when no less than five separate artists had hit recordings of "Mack the Knife", which had recently become popular in an Off-Broadway revival of "The Threepenny Opera", which, as we all know, had originated in Berlin, 30 years before.

The principle is, when a popular singer records a popular song, you'll be able to sell a lot of records. It still holds true today.