Here's a newbie point of view. I got my K701s after only hearing the shitty apple earbuds. They sounded like heaven! However, I found that I got somewhat fatigued because (to my ears, my PERCEPTION of the sound) the cans were a bit bright. After reading stuff on head-fi (yes I bought into the hype) I played them continuously for 300 hours, with short listening sessions every so often. After a while I found that they weren't as bright and the bass had beefed up slightly.
Whether this was a false perception, my ears getting used to the sound or whatever, I don't know, but that's how I perceived it.
I feel like the headphones themselves changed, because I didn't change the source, amp, or cables, but I know the power of the brain in deception (hell, music isn't even real, its just air molecule vibrations).