Maybe we're defining "killer app" differently, but over 80% of US households had a radio in 1940, a decade prior to the start of rock and roll.
I think of "killer app" to be something that drives the adoption of the platform or whatever. "Why should I buy a PC? Oh, because Lotus 1-2-3 is awesome." Nobody was buying radios because they wanted to listen to rock and roll music; they all already had radios.
As has been noted for radio, 55% of American homes had TVs in 1954 (rising to 83% by 1958). This was an increase from 0.4% in 1948. During this time of rapid adoption, the most popular shows were primarily variety shows and eventually sitcoms (I Love Lucy).
Soap operas have been a staple of daytime television since the early 1950's, but have never even been close to the most popular. Therefore, it would be hard to call them a "killer app".
I think of "killer app" to be something that drives the adoption of the platform or whatever. "Why should I buy a PC? Oh, because Lotus 1-2-3 is awesome." Nobody was buying radios because they wanted to listen to rock and roll music; they all already had radios.