Do you recognize the image above? This was Yahoo, on December 20, 1996.
I cannot help but see a distinct similarity between Yahoo (and other portals of the day) and the App Stores of today. Yahoo was trying to solve a real problem - discovering new content on the Internet was hard and a structured, categorical listing seemed like a good solution. This was until the likes of Google came along and completely disrupted the discoverability mechanism.
App Stores of today are doing something similar -
The problem with this approach is that it does not scale. Mobile applications, like the Internet sites of the 1990's, are set to explode in the next few years. The fruits of human creativity and ingenuity cannot be contained within 23 well-defined genres. Moreover, listings do not provide a way to discover content that is embedded deep within the walled gardens of the apps.
This will inevitably change. Companies will soon discover that it's in their best interest that their customers (and soon-to-be customers) discover their great content through third party channels. Customers will demand it and some company out there will make a lot of money off of it.