Historically consumer audio gear is not grounded, instead double-isolated because of the ground-loops that occur.
Power amp, tape player, turntable, TV, DVD player etc. would be connected together and lots of mains hum results.
You would have to use balanced audio connections instead of single-ended RCA jacks, so added cost there they avoid.
Really old audio gear from the 1950's or so, there was no earth ground in North American outlets. So they manufacturers used the "death cap" to stop RF and noise from being a problem.