2.6 is a bridge to 3.0 -- it implemented some 3.0 things, but kept a lot of backward compatibility. If a project can't convert to 3.0, they could convert to 2.6, which would then make the eventual 3.0/3.1 migration easier.
From the release notes: This is the second bugfix release of the Python 2.6 series. Python 2.6 is now in bugfix-only mode; no new features are being added. Dozens of bugs that were reported since the release of 2.6.1 have been fixed.