My take on it: Kids aren't bumping open headphones to and from class, on the subway, on the bus, or on foot around their neighborhoods. The Beats/Fashion headphone phenomenon and the rapid expansion of smartphones as PMPs has pushed a lot of new old players into the game. By "new old", I mean that companies that have been making competent audio products for decades - just not headphones. Focal and NAD are just the latest two. They have to get into the realm of headphone production because that's where profits are being made and business is being done...but more importantly its where companies are staking their brand recognition.
By and large, these new models that are coming out (at a rapid fire pace) are low impedance, high efficiency, closed on-ear and over-ear models. This surge of models is happening coterminus with the new Harmon research coming out and the Olive-Welti-McMullen research to find a new target response curve. Market forces and economics + quality audio and acoustics research = a lot of excellent closed phones, in sequence, with a lot of turnover. I think Tyll's reviews are just reflecting this.
On the last point, I think that companies are going small on the earcups because it's easier to assure a proper seal on a smaller cup than a larger cup. You're damned if you do, damned if you don't; either the persons ears won't fit because the pads are too small, or the fit is too positional and head sized sensitive because the pads are too big. They are erroring conservatively, in part because a youth audience is pushing the aforementioned beats/phones markets. Better chance they'll have smaller ears.
