There is plenty of exploration in modern MMO's if you sit at the top of the player curve. Unlike single player games they often have vary little documentation or handholding it's only the shear number of players that makes most secrets leak so fast and more importantly you dont't need to read all that player documentation of you don't want to.

A great example of this might be haste vs crit vs power. There are generally trade offs between them and the game in no way says which is more useful per point. In large part because the math depends on play stile, spec, and the dynamics of a specific fight. Still players often spend a lot of time trying different optomizations and building different simulations based on different assumptions. End result tens even hundreds of thousands of hours of experementation that ofen gets tossed out after each patch.

And because players will find this crap out on there own games have become vary vague with exactly how things work or what they changed. Aka "spell power less useful for ability X" which says vary little overall.