My question: What constitutes "difficulty" in a video game?

Nearly every instance I see of "difficulty" being described these days can be boiled down to essentially: Speed. How fast your reactions are, and how quickly you can button mash, and that's about it.

Personally, I blame the interenet for at least some of this. Since strategy sharing has become so awesome, fewer and fewer things are being made difficult in terms of strategy or puzzles, because most developers think that everyone will just google the solutions rather than work them out, but does that really only leave us with pure reaction tests as the only form of difficulty left in gaming?