Two examples in the last 4 days:
1: Several walkers on a canal path going in the same direction as me (on a bicycle). I shouted for them to move. One doesn't - the one with the headphones. I had to get within 3 feet of him to hear me.
2. cyclist on a mountain bike and a child seat on the back. He was shifting. I caught up to him and as I pass said something along the lines of "you're giving it some with that on". I got a blank look back. He had earphones in. He took them out. I repeated the words and he understood.
Fair points, but I don't think they refute mine.
In those cases I think it was much more likely they were too self absorbed, and the music was clearly contributing (possibly heavily) to this, rather than the music was actually blocking out the sounds. This is obviously something to be wary of when listening to music when riding - that you don't let it distract you rather than it preventing you from hearing. But I don't think music is the sole contributor to such behaviour. Been plenty of times when I've been riding the stretch of shared use cycle lane that makes up part of my commute where I've said "excuse me", rung bell and then even shouted at someone walking in front of me blocking the path - and they still haven't noticed me until I've crept past them - and they've not had headphones on.