You want the real answer? It actually just struck me that there is a very specific reason for removable power cords.
The products made are international.
The power cord which is packed with your receiver is a USA power cord. But, there are a dozen plus different types of outlets throughout the world, and the power supply built into your products these days are designed to handle 120/220 current without issue. So, while the power supply handles whatever voltage it receives (more or less), the power cord can't magically switch to all these different outlets if it is hard wired to the chassis. The manufacturing line would need to specifically put a different power cord on every final destination country as part of the manufacturing process.
Now, it's part of the packaging process. You get all your Euro cords, Asian cords, American cords, etc., that get dropped in with a manual and the proper box.
If you move from one country to another, you swap the cord and are good to go.