@zatarot are you really going to go back and read some obscure comic book character's 20 years past backstory to "read from the beginning"? If you didn't know anything about Batman, would you go pull up comic books from the 1960s? Or would you want to get a gist of who these people are and what they are doing so you can follow the story with the book you have?
Everyone knows batman already, so you can just hop into a batman story just fine. But longer running shows people may not be able to get their hands on older issues, and therefore can't read up on it.
Thus, recaps at the start of story arcs.