That's a heavy assumption. If you're wrong, the result is that Gitorious doesn't fit for potentially a large number of developers.

In my experience, sampling developers with whom I speak on a regular basis (and myself), private repos on GitHub are very popular. This is especially the case for web developers, as open sourcing web apps is less common. It's nice to have all of my open source stuff in the same place as my closed source stuff, such that I (and anyone I deem worthy) can interact with both in the same way.