Now that DVCS tools like Git and Mercurial are available, and incredibly easy to set-up and use, there's really no excuse for even a team of 1(!) not to use source control. It's not about size of team, it's about having a commented history of your changes and the ability to support workflows such as fixing production issues whilst working on a new release, and tracking the state of the source code for different versions.

If I were offered a job in a team that had got to that size, and not one of the developers had suggested using a VCS, or if "management" had prevented them, I'd turn it down flat. It's just not an acceptable way of working these days.