Why Is Star Wars Episode 7 PG 13?

It's strange that a the new new addition to the Star Wars franchise has been given a PG 13 rating, especially with all the other installments being PG rated, but is there a solid reason why the Motion Picture Association of America have given Episode 7 this rating?
The primary reason for the MPAA giving a PG 13 rating is down to "Sci-Fi Action Violence". But why weren't the other movies rated PG 13? The previous Star Wars movies racked up some serious body counts, but with pretty much no on screen blood at all because lightsabers and blasters conveniently cauterize wounds. So could this mean that this new Star Wars movie is a bit more bloody? Or are the MPAA just kicking up a fuss over nothing like they usually do.
Either way my excitement for this new movie is like nothing I've ever scene and even with the PG 13 rating I have high hopes that it will shatter box office records, with over 50 million dollars already made in pre-sales. Could Star Wars Episode 7 top Avatar?