Programmers count from 0. :-)
All versions of my (only) CPAN module had no known bugs when I released them (and the test code to show that the known bugs where fixed). That didn't really mean they had no bugs.
You point about API changes is valid, but that an API is "complete" doesn't mean it's "done". It takes a LOT of testing and tweaking to get an API "just right" - so I myself prefer to keep the right to make "minor" changes to an API for quite some time.
The 1.0 version number is arbitrary and for marketing purposes only. The associated software is never bug-free, never finished, and ususally deprecated within a couple of weeks. Programmers should know better than to trust a version number.