I believe it's just that GoPro + Internet allows for more action sports footage from many more perspectives to be broadcast to a wider audience compared to what was available ten years ago. I know theberrics.com uses GoProp for a lot of their footage.
They are Block--Element__Modifiers (BEM). It's a style of css meant for developer readability and code reuse.
In this instance you have the following:
.btn { //the base code for a button }
.btn--s { font-size: 12px; }
.btn--m { font-size: 14px; }
.btn--l { font-size: 20px; border-radius: .25em!important; }
Now if I want to make two buttons, one with small font, the other with large font, I can simply do this:
<button class="btn btn--s"></button> <button class="btn btn--l"></button>
Personally, I like writing with BEM methodology rather than repeating style rules over multiple classes.