Personal stereos have been around for a while now. That it's a shiny Apple product driving the headphones rather than a ubiquitous 80s cassette player shouldn't make the slightest difference in terms of your awareness of your surroundings. It seems odd that there would be an increase in incidents.
Back in the days when I was regularly walking non-trivial distances or using public transport, I'd use a cassette and later minidisc player most of the time. I'd simply look both ways before crossing a road, as I was taught to as a child, which is what I do even when I can hear unimpeded. My partner removes her hearing aids (effectively giving her silence) when walking around outside, as the confusing monaural mush of traffic and wind noise is overwhelming and not particularly beneficial, and hearing aids prefer not to get rained on. She uses the same looking-before-you-cross technique. It appears that that has gone out of fashion.
Anyway, I'd have thought mobile phones would be more of a problem. You're more distracted and your hearing is less obviously impaired. They certainly seem popular amongst the pedestrians I have to take evasive action for.
I've never used headphones while cycling. I'm not especially averse to the idea on awareness grounds, though I wouldn't bother in city traffic because the noise would drown out the music, but the practicalities of headphones that stay in my ears while moving around sweatily have thus-far thwarted me. I don't see it as any different from using them as a pedestrian, or having music playing in a car. No audio, no problem - as long as you're making decent visual observations.