Seasons three is upon us and some of the new changes that came with it will give you even more choices for each build. Allowing you to specify your build and perfect your champion to your preference.
It's all about choices. Choices in your masteries and your builds that cater to your individual playstyle. Certain masteries are a little too role oriented, so Riot Games has expanded them to appeal to different roles. Some masteries have also been nerfed and replaced with others like Siege Commander was replaced with Tower Shield and many more.
Also, some champs required players to spend points on masteries that aren't really beneficial to the player. So players would have to purchase all these unnecessary masteries to reach the one they initially intended to purchase. Riot have tweaked those settings, making certain masteries less dependent on others.