Re changing trends in what sells - much is to with the brands/models in play at the time, and the resulting coverage/Awards those designs get.
For example, a few years back you couldn't get many good-quality in-ear headphones - they were typically cheaper alternatives, some not much better than the ones you got bundled with a player (sometimes worse!).
However, then some of the bigger names in audio - including Shure and Sennheiser (both of which were already making pro-quality earpieces for musicians etc), plus hi-fi companies such as Klipsch - started making more serious in-ear designs.
Couple that with iPod sales going through the roof (and selling to people after grown-up sound, not just portable convenience) and the in-ear boom was born.
The 'mini' designs have been fuelled by fold-up designs such as Sennheiser's PX series and (at a later date) Grado iGrados, which were about the only way of getting great on-the-move sound for under £50, apart from those super-cheap in-ear options.
However, with such a wide array of in-ear designs - plus those fold-up designs not always being the most commute-friendly (as they're typically open-backed, so leak out sound) - they're not as popular as they once were. Still room for a new, popular model to come in and change that, though.
Meanwhile, people are rediscovering the joy of larger, hi-fi headphones for both home and travel use. With more of us than ever living in smaller spaces/closer quarters with families etc, it gives everyone the opportunity to enjoy excellent-quality sound - from laptop, iPod or hi-fi/home cinema kit - without disturbing the neighbours/loved ones.
Re wireless headphones - arrival of Bluetooth wireless headphones had a boost, but there are still v.few convincing models (though again, a great model could change that).
And no, the figures do not include those headphones that come bundled free with portable gear. Most of which are best binned!