More multiplatform books--or are they books?

Once again we hear of a publishing project which sounds more like a business plan than a traditional book publication. Publisher's Weekly explains that the new Mackensie Blue series aimed at tweens--those 10 to 15 year old girls who are such a media target these days--will utilize websites and music deals as well as producing a series of books about Mackensie Blue, a heroine with a desire to be a rock star. From all indications, this type of publishing is going to be increasingly profitable and therefor will grow over time. We can't help wondering how long these books will last, but perhaps immediate profits are more important than longevity.