"Your headphones suck! (pointing K701) this thing does not have any bass!"
*gives him D5000*
"OK... it is much better, but still need more bass"
I know, there are such HUGE (yes, capital words for emphasis) market for bassheads, and -not just headphones- many consumer audio devices are tuned for more, more AND more bass.
No need to look further, here in Head-Fi we have some exotic, super expensive things like Audio Technica L3000 to cheapy Sony XB series. One of the most popular closed headphones in Head-Fi, Audio Technica M50, also have such large amount of bass. Most of Ultrasone headphones have one of the biggest bass you can ever heard on headphones. Not to mention the most popular beyerdynamic headphones, DT770 variants are famous for bass as well.
Outside of the Head-Fi, the trend is very clear; pretty much all celebrity headphones have such gigantic focus on bass quantity, and most of the headphones are quite bass heavy except perhaps Bose ones (maybe it is one of the reasons Bose headphones lost popularity outside of their noise cancelling lineups?)
Some people say that's how the sound supposed to be heard like from speakers. I disagree. I don't get such strong bass response from both expensive B&W 700s+Denon setup nor cheap JBL+H&K setup. And if you have ever gone to live concert, the bass on most of consumer-focused headphones is just not normal.
Yet, there are so many people like bassy headphones, and there is no doubt; I believe majority of people are bassheads. Now the question is, why?