Well, pytz actually is technically flawed at the moment because it cannot read TZif Version 2+ files, so it breaks for dates >2038 (and it would break if you tried to point it at system data generated with zic's "slim" mode), see this: https://github.com/stub42/pytz/issues/48

But you are right that pandas' use of pytz is benign and as far as I know doesn't suffer the same usability issues.