My personal preference is not to wear earphones, for the lack of distraction and because I like the extra input. Not so much that I think my hearing always tells me about cars, but I hear changing engine notes etc. It's just extra info, extra input.
Since my head issues, I can't do 'quick' glances behind anymore, it has to be slow head rotations. So I always check at some spots, but I rely more on my hearing than I used to. Yes, I can hear bikes coming up behind me. Yeah, I'm Matt Murdock in disguise.
But it has to be down to personal preference. I think that they can be a distraction and if people are to use them, they need to be aware of that, just like using a radio in a car.