Over on the Swivet, guest Courtney Summers blogs about some myths about YA.
Honestly, I don't know that these beliefs are common and I don't know that they are totally wrong, either.
For instance, to what degree can you swear in a YA novel? In any novel?
I find swearing, by which I mean the literal depiction of particular swear words, to be intrusive and to negatively affect my reading experience. Sure, most people swear, but most people poop, and most people pick their noses, and that's just to get started, eh? We don't generally show pooping in stories, at least not as much as we actually do, because it's pretty boring and icky. So is swearing.
The question is, what function does it perform in the story? I'm not really talking about an occasional "Damn", I'm talking pervasive f_ing foulmouthedness. Hollywood types think it makes their show "edgy", or gets them the coveted PG-13 rather than the PG the story would deserve without the gratuitous nastiness.
In any case, I'm not sure that anyone believes you can't get away with gratuitous swearing, sex, drugs etc in YA, since clearly there are books that do.
I'm also not sure that you actually can get away with them, since they are so easy to do wrong, and if you do do them wrong, your book will not sell to libraries and will die a sad, lonely death.
My suggestion - write an awesome story, where the characters are so frelling fascinating that the reader won't notice that they aren't shagging each other and vomiting meaningless epithets and imbibing mild organic poisons.
Do that, and don't worry about the myths - you'll become a legend.