He's NOT having "the book thrown at him." He's being charged with 2nd degree rape, which, among other things, covers statutory rape.
If there were evidence that he forced her, it'd be 1st degree. Second degree either means statutory or he took advantage of her in a state where she couldn't consent, such as asleep, passed out, etc. Given her age, they wouldn't have to prove anything except that he had sex with her. The other charges...2nd degree sex offense and such indicate that he did more than have intercourse, but other sexual acts any of which would be illegal based on the girl's age alone.
Now chances are, they are being conservative and charging him with statutory because they don't have solid evidence of force, even if that is what occured. Get him on arrested on what they can prove and build up the case from there, if possible.
Maryland Judiciary Case Search
But then why is he being held without bond and charged as an adult? And why the assult charge?