A list of stdlib modules/extensions is IMHO problematic for maintenance, esp. if you consider that not all modules/extensions are installed on all systems (both because dependencies aren't present and because packagers have decided to unbundle parts of the stdlib).

Wouldn't it be sufficient to somehow mark the stdlib entries on sys.path? Although that might give misleading answers with tools like pyinstaller/py2exe/py2app that package an application and its dependencies into a single zipfile.