Ah. I don't understand this stuff, but I somehow got the impression there was potential for damage if something rare went wrong. But hey, that's life!
There are 2 separate things in this DC story.
1: When an amplifier is purely DC coupled AND the device connected to such an amplifier has a DC voltage on its output then that DC voltage is also amplified.
In such a case (a DC coupled amplifier) it is highly recommended to have DC protection on its output.
Such a protection usually kicks in when more than 0.5V DC is detected and disconnects the load (speaker or headphone)
2: When a source has a DC voltage on it and is connected to an amplifier that is not DC coupled then the DC does not matter that much.
It can cause a loud 'tick' when switching inputs or a 'thumb' when switching the source on when the amp is already active.
3: When the output of an amplifier is DC coupled, so no output capacitor, which is often the case with many amplifiers then, when something in the amplifier fails catastrophically there might come DC on its output (depends on the actual type of failure).
When such an amplifier does not have DC protection then it is possible DC appears on its output which potentially could destroy a woofer or headphone driver.
This is a design choice.
When an amplifier already has a start-up/or quick switch off relay in it (such as Schiit amps) then it baffles me something as simple as DC protection isn't implemented at all.
There are very chip IC's that have delayed-on/quick-off and DC protection in it that costs next to nothing. The relay is the most expensive part and is already in there.
Such a DC protection could save expensive drivers in case something goes wrong inside the amp.
Admittedly the chances are slim but for almost no extra costs an amplifier manufacturer can protect drivers from users of their amplifiers damage to their drivers. A design choice.