It's all about the degree of violence represented in YA fiction at the moment. Basically, one well known book reviewer wrote an article damning YA fiction for it's use of violence - we're mainly talking rape, drugs, alcohol, self-harm. Since then there has been a huge backlash, with the vast majority defending the benefits of the way in which, and the degree to which, violence is being portrayed.
If you fancy a read, there's a link to a blog about it below, which contains links to some of the arguements.
A good read if you fancy it!