Sound is a wave (specifically, the effect of the sound wave travelling through the air). A wave hitting something like Sonic Boom does would exert a certain amount of force upon that something, hence why it does damage, although it somehow doing fixed damage to everything makes no sense, as the ability to react to that force varies greatly between what you're hitting (I'm a Physics minor).
As charking said, it doesn't work. It's a flawed system currently, and fixing that system is a Good Thing(tm).