I don't think it is really a song has to have one; but more that you have paid staff writers most of the time writing the songs and so if a format sales they just rinse and repeat. How many times do you hear music today and think before the performer starts singing; that;s so and so, no it;s just the clone factory at work. Some of the biggest song's ever do not have a chorus; Freebird, Stairway to Heaven, Yesterday, Bohemian Rhapsody, but they all come back to the main idea which makes them memorable; plus in all of these songs there is an undeniable and unforgettable haunting melody, They can all be played without any vocals and automatically they are known. which in most songs even the uptempo tunes the lead instruments are what really make the song so memorable. It will be a lead guitar lick, or a piano solo, or group harmony. When people say Van Halen they automatically think guitar, no matter how many #1s they had with vocals. Really the only songs that rely totally on lyrics are Love songs with bare bones instrumentation. Christian music, or message type song. That does not mean the lyrics are not important; but when you look at most #1 songs, it is the melody; that you will hum even when you do not know the words.

My Tunes

Psalm 57:7 My heart, O God, is steadfast, my heart is steadfast; I will sing and make music.