You can't go a day without hearing a Beatles song somewhere (unless you listen to an ipod all day), just about every other commercial has one (Target, Nike, etc). ESPN highlights, Movie soundtracks, TV show songs, etc.
But i think the biggest selling factor is people actually know the words and the songs are easy to sing along to. Who doesn't know the chorus to Ob La Di Ob La Da or Hello Goodbye or Yellow Submarine? I haven't been to a wedding that didn't play "When I'm 64". Most 10 year olds have heard Come Together. Who knows the words to "Run to the Hills"? Who can hum along to Dragonforce?
The same goes for the Stones or Zeppelin. May not be everyone's favorite band, but the songs are instantly recognizable. Kids may not know it's the Rolling Stones, but they know the song Satisfaction.