just optimized differently.

But then, I guess you could also say they are really just electric motors / generators (another pair of items that are the same thing optimized differently) that don't spin.

But speakers/microphones are REALLY the same, and motors/generators are so much the same that you can easily test the fact that they are. When I was a little kid, Grandpa had me put a meter on the input leads to a little electric motor and spin the shaft. Sure enough, AC current. I miss the guy. He's been a blue ghost sitting behind me for decades, giving me a hint or encouragement when I needed it, but that's not the same.