If its only coming with 3.2.3 it will break many existing tools.(think django)

If you see MAC, it does come with lower versions of python too, so it supports older python projects.(python2.7, python2.5 based and doesn't break the system)

Latest Ubuntu might well come even with lower versions of python too - as many Ubuntu apps and tools itself use the lower versions of python. But the default python will be 3.2.3

To use the right version of python we have to -

Manually install older versions if it doesn't have one.

And do symbolic Linking the installed versions to /usr/bin and set $PATH appropriately for the correct Python version we need. Just use them as python2.7 python2.5 python2.6 while calling your scripts.

Also see virtualenv.