These frequencies sound good to human ears.
So, when someone compares Beats to non-Beats, they hear that those frequencies are louder and the very fact that there is a noticeable difference is enough to create the illusion in some gullible people that Beats 'sound better'
Of course, in the long run, they don't.
I'm not defending Beats at all, but I'll defend that low frequency / high frequency setup all day. Not everyone listens to classical.
The problem is, a lot of modern music has this same curve (the "smile") heavily applied to it already, so it can disintegrate into a mess quite quickly.
It depends which model you buy. Their 'Pro' model is marketed towards sound engineers so I doubt they mess with the EQ on those. They also claim they are "The Headphones Used To Mix In Every Major Studio." which I seriously doubt. AFAIK it's always recommended to mix with monitors, not headphones.
In reality of course, engineers typically use headphones that sound as boring and "lifeless" as possible, for obvious reasons.
Ironically, they often also buy (relatively) cheap ones, as they get used to destruction.