The problem often comes with data. If the service collects user data (and most services do), it is often a real problem when it shuts down. Suddenly none of the links work, the data is gone, and any reputation or network built up is also hard to retrieve.
If the service was offering a discrete operation on local files (by analogy with a desktop app or a restaurant), then it wouldn't be a great problem if it shuts down, you just find another.
However, going back to this service - someone using this help service to help others might build up a stellar reputation over 10 years, only to have the plug pulled on all their posts, and all the content disappearing or at best losing all its links in when Google decides to move on to Google++ and retires it.
If the service was offering a discrete operation on local files (by analogy with a desktop app or a restaurant), then it wouldn't be a great problem if it shuts down, you just find another.
However, going back to this service - someone using this help service to help others might build up a stellar reputation over 10 years, only to have the plug pulled on all their posts, and all the content disappearing or at best losing all its links in when Google decides to move on to Google++ and retires it.