Maybe RedHat, but it's about it. Even Debian Stable comes with 2.5.

BTW this rant about impossibility to upgrade is a classic one and nonetheless wrong. You're perfectly able to install new versions of python, or perl or whatever given that you do that in /usr/local to keep the official version alongside the new one. I do this all the time, my system comes with perl 5.10 but I regularly install the newest releases in /usr/local, or even development versions. No problem.

CentOS 5 (even latest 5.5). You can install python25 or even python26, but 2.4 always stays as a default.

As long as you know about it, you can fix scripts, but any downloaded program needs a change in shbang line, or at least running explicitly via python-2.X.

But yes, "most Linux distros" part is completely untrue. Most have at least 2.5 - or higher.