What is a YA novel anyway?

I finally decided to read Hunger Games and in less than a week finished the series.  I liked it so much that I passed it on to my husband.  He reads a lot.  He's the adult male version of Rory Gilmore.  I'm pretty sure he took up smoking at work to get more reading breaks.  So its high praise to pass a "kids" book onto him.  Like many adults, he's read Harry Potter, but mostly he sticks to the grown-up sections of the bookstore.  He's not finished yet, but he's hooked.  And something's bothering him.  He keeps asking me what makes this book YA?

At first I assumed he was horrified at selling a book on this concept to teens.  Not that he's a censor, but its a far cry from Judy Blume, you know?  But that wasn't it.  He did thing the concept was adult, but he didn't care who read it, so I told him the age of the protagonist.  Turns out he's a little peeved that a book with such "simple, elegant prose" and interesting plot elements was being marketed to teens.  Remember the little debate going around online about teen boys and YA?  It's interesting the number of adult women I know who have read the books or Twilight or the Mortal Instruments.  It's not just teen boys ignoring YA, its adult men too.  Every time my husband mentions the YA novel thing I'm struck by his obvious misconceptions.  Hunger Games is too well-written, too compelling, too innovative to be YA.  So does that mean the average person assumes YA is "kids" books written for a less sophisticated audience and therefore not well-composed or interesting?  So do YA authors undermine themselves by labeling their books YA?  Or will really good books always breakout?