Why not? My wife and I each bought a Deathly Hallows. It's not gonna be a NYT Bestseller, though, because it's a "children's book."
The book that will probably set a single day and one week sales record, the book hundreds of thousands will line up for at midnight won't be the Number One book on The New York Times Bestseller list? That's right because Harry Potter and the Deathly Hallows is a children's book and those books don't count.Also mentioned in the article as screwed by this policy is His Dark Materials, a series I've heard good things about, but not much, because it couldn't be a bestseller either.
The article points out that if this ban had been in effect when the first Potter book was published, the series wouldn't be what it is today.