Here's a quote from the Wall Street Journal on Scholastic's plans for Harry Potter:
"The small print: Scholastic hopes the latest Potter book will raise consumer awareness of all Scholastic products, including its lineup of educational literature and children's books. Still, the company will need to seek alternate revenue sources after the seventh and final book in the series is released."
This is a lesson to learn from watching the marketing of Harry Potter books. As good as sales are for the series, there is an even larger revenue stream from the movies, merchandise and mostly the increased sales of all books in that age group (young readers and all ages ADULTS).
At the Barnes & Nobles store I visted during the launch, there were kids and adults in the aisles and other common areas, sitting in the cornes, on the benches, on the floor and right in the middle of the doorway. There we even more outside.
Almost ALL of them were reading.. and carry more items to purchase with their reserved copy of "Harry Potter And the Half Blood Prince"