What's the 'best' headphone? If you asked 1000 people this, most would probably say Bose and the second most popular answer would probably be Beats By Dre / Monster. Beats would probably be picked first among a certain segment of the population, those from 13-25 years old. Their answer would be based overwhelmingly on one thing... marketing.
If you asked them what other brands they've tried the overwhelming majority would be hard pressed to name a brand other than brands sold in Best Buy, Fry's, HH Gregg or Apple. While some of those brands do make great sounding headphones, (Sennheiser, Sony) the models sold in these stores are the models predominantly made for the average consumer, not the higher end models that some of these brands also make.
When you buy a car from a dealer and want the stock high-end audio system, it's usually Bose, right? (Although now some car manufacturers (and electronics) are now available with Beats Audio.) Yet when you take your car to an aftermarket car stereo shop and put in a much better sound system you don't choose Bose, right? You usually choose something like Polk Audio, Infinity, Alpine, Diamond Audio or Boston Acoustics. My point being that Beats and Bose are better sounding than your average department store speaker but there is far more out there that most consumers aren't aware of.
So then why do most consumers so quickly jump to believe that the same brands you'd replace in your car to improve the sound would also make the best headphone on the market? Marketing and ignorance. The average consumer isn't aware of well respected and reputable audio brands because they don't place ads in your airline seat-back magazine or numerous other non-audio magazines.