My apartment has a circuit breaker in the breaker box but my audio is not grounded.
Dazzdax, I am going to take a guess here. The receptacle your audio system is plugged into is an old 2 wire type, no equipment safety ground. If all your equipment is plugged into this one duplex receptacle the odds of you getting hit by lightning is better than you getting shocked from your audio system.
Not sure why audio equipment manufactures just don't make all their equipment with double insulated power wiring and eliminate the need for the equipment safety ground altogether. Especially the power amp manufactures that have their signal ground and safety ground commonly connected to the chassis. Then in their owners manual tell the user to use a ground lifter if they experience a ground loop hum problem.
I would agree with Gs5556 post about the signal ground and the safety equipment ground. But in some equipment, especially power amps, the signal ground and equipment ground are connected together putting them on the same ground plane. And for some....the dreaded ground loop hum.
http://www.soundstage.com/weaver01.htm