I think the problem is there even if you're focusing on the One Thing. Look at Github. They have issues, wiki, gist, pull requests, search, repo browser, keyboard shortcuts, private repos and so much more. That's still within the One Thing.

And of course, Github built those things over time. But the question that still remains, especially on the early days, with limited resources:

What new feature should we add next to this one thing?

from a list of dozens of features that customers are screaming for... Shall we add a native app? or should we add Facebook integration? Should we add some gamification elements or redo the homepage to increase conversions? and the list goes on.