I never really understood this. Sure, changing the version in one place would be better and I would do that if it was possible with the current Python tools. But I have seen insane setups to achieve this, parsing __init__.py with regex from setup.py, using third-party dependencies that do only that, sometimes scripts with hundreds of lines included in the distribution to support it.

Is changing the number 2 places really that big of a deal?

You should have a release checklist anyway, with steps like sending an announcement email or tweet etc. How much time does this really save, at the cost of so much complexity?