Amazingly people still use Python 2.3. With source downloads you can't tell what platforms use, but you can with binary downloads. One of my projects is a Python wrapper for SQLite (APSW) for which I also provide compiled Windows binaries for every Python version from 2.3 to the latest, and 64 bit for some of them too. It is very amusing to me that some people want the latest SQLite while using a positively ancient Python version.
Google code shows download counts so you can get an idea of popularity of each release for Windows developers:
https://code.google.com/p/apsw/downloads/list?can=1&q=&colsp...
I've since moved the project to github which doesn't show the download counts for releases.