A NAD amp I was working on recently is the same.
There's a latching power push-button on the front, but that just brings on a 5v standby power supply.
This powers up a little microcontroller which is listening for one of the source buttons to be pressed, and also to the IR remote control receiver.
To power up the main PSU, you must either prod one of the input selector buttons, or use the remote.
That closes a relay, enabling 240v to the main transformer.