App Store for Web Apps

The "app store" concept has been very successful for Apple (iTunes App Store) and Google (Android Market) in the mobile space. But, what would an app store for web apps mean? During Google's announcement for Chrome OS, Sundar Pichai, Vice President of Product Management, said "the Web offers hundreds of millions of applications" and that Google's job will be "to make people aware of them." (starts around 48:38). "Hundreds of millions" is a big number but in the context of 1.7 billion Internet users worldwide (with many users using multiple applications) the arithmetic "smells right." So, what would a web app store do? The purpose of any app store is to reduce the friction of connecting a user to applications. What are the areas of friction that can be greased?