Not sure why you're being voted down. Distribution channels don't just spring out of the ground overnight. Apple's promotion of iTunes and the App Store created a critical mass of users willing and able to spend money, while Apple maintains that by creating mechanisms to satisfy their demand for apps and content.
Because if people are searching for a product, they probably already know about it and it is hard to call that "promotion" unless you squint really hard in which case, Google is offering free promotion to everyone!
