For future reference: you must say my name 3 times when you wish to summon me forth.
Believe it or not, I'm not familiar with the internal topologies of every receiver out there. So I can't confirm your blanket statement of a blanket statement.
That said, you are on the right track. An op amp controlled MOSFET pair (what you're referring to as a push-pull configuration) has a much easier time handling high currents vs. an integrated circuit doing the work. But that's mostly due to the size of the MOSFET components, and the heat handling which comes with scale.
It's worth noting that TI now has a single chip, class D amp, which handles 2 channels of 300 Watts each, and is stable into 4 Ohms. So on-chip amps are coming along. Class D helps a lot, because it is never in the the half-open states that produce the most of the heat. When the "valve" is closed there's no current flow, and little heat produced, when fully open there's actually less heat produced. But in the in between, where AB amps spend most of their time, that's where the excess energy has to be siphoned away as heat.
