Never seen a top racer use headphones. I have never used one in a race, and would never consider wearing one. We look dorky enough already, and the headphones, IMO, make it worse.
I want to be talking to folks around me while I am running, saying thanks to volunteers, spectators, not being in my own little world during a race. But what do I know. .
Perhaps you didn't realize it's possible to speak with headphones on. They don't actually block speech or send the sound out to other people - they just send sound to your ears. So you can say "Thanks" or "Water" just fine with them.
It's even possible to hear things with headphones on if you set the volume low enough. Believe it or not it's true! Your hearing won't be as acute as if you didn't have them, but you can hear a lot.