Having worked in children's books off & on for 10 years, I would say the book is not appropriate for the majority of 10 year olds. Greg (yes, I've met him numerous times & can call him that) didn't intend the book for kids, so it does have mature situations.
That being said, every kid is different. I read the anthropologic porn of The Clan of the Cave Bear in 5th grade, knew it was totally inappropriate, but don't think it warped me too much. :)
& definitely read all the Oz books if you haven't. The Tin Woodman of Oz is probably the best of them all. Enjoy!
If you live in NYC you can find a huge amount of Oz books of all sorts at Books of Wonder. & yes, I'm shilling. It's a great store. :)
It's hot and it's monotonous.
I want my glasses.