It struck me as I was watching an episode of season two that the theme of parenthood/parents was a dominant issue for most the main survivors and the reason as to why they were on the flight:
Jack - he was looking for his father
Kate - she was on the flight because she had killed her stepfather
Sawyer - he was there because he set out to kill the guy who had an affair with his mother
Gin & Sun - they were escaping the oppression of Sun’s father
Shannon & Boone - Shannon’s life started to go wrong when her father died, Boone was on his way to rescue her
Michael & Walt - Michael was on the plane because Walt’s mother had died
Claire - she was initially on the flight to adopt out her child
John - although not directly, but his life had been changed dramatically when his father deceived him when he took his kidney
As for Hurley and Charlie, I don’t know that much about their family history so I’m not too sure. Is this theme of some significance to the story or just mere coincidence?