I also think that the song Baby makes Justin Bieber very rich. "Baby" has been an international hit, all of the kids here in my country know that song and even dance while listening.
Yes Justin has done so many things in a very young age. 50 billion..you gotta be kidding. I think Baby, One time and One less Lonely girl are the songs that made him popular.
Yes , it's the "Baby" songs that has made him very popular, especially among the very young audiences.His good looks and dance moves are also a big factor.