The README is always included, as indicated in the article. Keeping tests on disk may be useful for the module developer, but it’s a crappy user experience for the end user. I don’t believe it’s worth the trade off, because it comes across lazy/unprofessionally. Imagine if Microsoft distributed their unit tests for Word in the release.

You’re right that many authors don’t tag their releases, but npm does. It’s another subject the greater community needs to address.