However, with the new toy "collaboration Distance" of Zentralblatt, it is easy to check that this is by no means exceptional - actually, within a half hour search, I wasn't able to find a mathematician to whom my collaboration distance was larger than 6 (if it wasn't infinity), regardless of research area or age, and the distance 6 was impossible to realize to people who are still alive. Here are some non-exhaustive examples:

Distance 3: Yurii I. Manin, John v. Neumann, Andrei N. Kolmogorov, Bernd Sturmfels...

Distance 4: David Hilbert, Friedrich Hirzebruch, Norman Steenrod, John F. Adams, Terence Tao, Alexander Grothendieck...

Distance 5: Elie Cartan, Helmut Hasse, Hermann Weyl, Emmy Noether, Stefan Banach...

Distance 6: Sophus Lie, Srinivasa Ramanujan, Bernhard Riemann...

I guess this proves that mathematicians are not always spending their time on useful things...