Applications on webpages will be distinctly different from apps on social networks. On social networks it’s like you’re setting up shop in a mall. All the plumbing is there and foot traffic is nearby, people just need something interesting to look at or buy. Apps “in the wild” will be different. Websites are cleared land that have interesting topography, but not of the essential utilities for healthy social living. But while Google does provide some management tools, they won’t come up with every sensible utility for a website.
I see a greater opportunity for utility based applications to do something interesting with the user data pulled into the website. Invite applications, mailing lists, and messaging services will help web masters manage their user base.