
Firstly, the first half of the movie is based around the origin of batman (where he came from) and how and why he became Batman. The reason for this is to let the audience know what they are watching, so the right people are watching the movie and will enjoy it. Origin stories are mostly about ordinary people suffering some a sort of transformation. Unlike some movies, the superheroes do not choose to become what they do. For example, Spider-man, he gets bitten by a spider which gives him special powers and abilities therefor does not choose to become what he does. But Batman on the other hand, does want to become a hero to save Gotham from evil and stop its corruption and ending.
Lastly, like all superhero films the typical conventions are that they have extraordinary powers, skills, wealth and technology. Bat-man has abilities no other average person has. For instance he is very wealthy, therefor most of his 'powers' where bought. He bought a cape made out of special material that can fly, his suit that a bullet cannot pierce and the bat mobile. All these things added to his strength and ability to defeat the villains and their 'minions'. Without these abilities the hero would be too easily defeated, the same goes for the villain, if they are weak they could be defeated too easily and the film would be boring. So the hero always has to have a weakness to create suspense within the movie.