I have a question on the need to provide a ground for each unit in my rig.

Power for both my receiver, Pioneer TX-540, and my turntable, Pioneer PL-510A, comes from the 'Switched' and 'Unswitched' power sources on the back of my amp, a Marantz 1070. Two pin power sources, no ground. The turntable has a ground lead integral to the RCA leads and that hooks up to the ground on the amp. The receiver has no provision for a ground other than the 75ohm antenna connection.

Is this normal with receivers? would there be any benefit running a ground lead from the receiver case to the ground on the amp? Or is it a case of 'if it ain't broken don't fix it'?

Thanks
Chris