One of my favorite things about cycling is really being outside — and hearing all the wonderful and crazy sounds is part of that. The birds chirping, the cars in the distance, the planes over head. Even in the city, for me it’s just part of cycling. Of course, I don’t go on really long rides, so maybe I would feel differently. (And I think the bike-speaker thing is cool, as long as you keep the volume reasonable).
Running is a different story. Maybe because I’m slow and gasping for breathe, but I don’t hear the glorious sounds of nature/the city when I’m running. I just hear my heart saying “I’m working really hard”, my feet saying “pound, pound, pound” and my knees/hips saying “ow, ow, ow”. (Ok, it’s not that bad, but I do mostly hear my own breathe and my feet hitting the pavement). So music is a welcome distraction. I do keep in both earbuds, but I make sure the volume is pretty low.