"...like class d amps. Someof the capacitors and other components are stressed to the maximum, all the time."
Output Mosfets connect output to positive and negative supply with duty cycle dependent on desired output voltage. When duty cycle is 50% average output voltage and current are zero. At this point Mosfets' current would be 100%, switching load between positive and negative voltage, if not for the fact that load is not resistive (speaker). Not only that speaker presents very high impedance at the carrier frequency (about 500kHz), but there is also low-pass filter between Mosfets and the speakers (Zobel network), that filters out 99% of the switching pulses. Voltage on the speaker becomes zero (with very small switching noise) and current thru both output Mosfets is close to zero. It is very easy to verify, just by placing hand on them, or measuring amp's supply current. My Rowland model 102 small class D amp total supply power was 10W with no signal (no stand-by) to 500W at full output power.
Switching devices in any electronics switch all the time, often heavy currents, and last for decades, including every computer where switching regulators often switch tens of amperes. SCR's in spot welding machines switch hundreds of amperes and also work for very long time. We don't have to look far - diodes in linear power supply switch large currents constantly 60 times a second.
To sum this: No, switching elements in class D amplifier are not "stressed" all the time, but even if they were it doesn't mean at all that they have to fail.