Why major version change, why 5.0 after 4.0.1?
What you're saying is that major number will change with time, not based on some groundbreaking updates. How am I supposed to know if I should be careful when upgrading from version 12 to version 14? Were there massive changes in between? All I know now is that half a year has gone by since last time I updated. Why would I care about that? Yeah, sure, I can read changelog for _every_ _single_ _library_ _and_ _tool_... Really? </rant>
EDIT: other than that, congrats on a new release. ;)
In the unlikely case that a new release causes code that worked in a previous release to fail, it's simply exposing a bug in either the new or old release.
Summary
Given a version number MAJOR.MINOR.PATCH, increment the:
MAJOR version when you make incompatible API changes, MINOR version when you add functionality in a backwards-compatible manner, and PATCH version when you make backwards-compatible bug fixes.
Personally I really hate how everyone (especially web browsers) blindly copies what Google comes up with, without putting much thought into it, whether it is UI changes, versioning or behavior changes.