While anticipation is high for the new Harry Potter book, there will be less Harry merchandise for sale. The release of “Half-Blood Prince,” the sixth of Rowling’s seven-book fantasy series, should confirm that Harry Potter mania is essentially a celebration of reading, a phenomenon created by children, not marketers. Demand for the book is higher than ever. Scholastic, Inc., Rowling’s American publisher, has announced a first printing of 10.8 million, seven times the first run of Bill Clinton’s “My Life” and 4 million more than for “Order of the Phoenix.”