Actually, the stable version of 4.2 is 4.2. Releases go through at least a month of publicly accessible beta and release candidate testing before the final release. Here’s where 4.2’s public beta testing started: https://www.ads-software.com/news/2015/03/wordpress-4-2-beta-1/ and you can see the other releases in sequence under https://www.ads-software.com/news/category/releases/
4.2.1 is just a critical security fix and one very minor code cleanup. Fixes for the known issues that can be fixed are in progress, but please note that some of the known issues are due to plugins, themes, and server configurations, not WordPress.
4.1.3 was a critical bug fix for the critical security fix in 4.1.2, but it’s not as well known because 4.1.4 was released as a critical security fix shortly after.
Remember, we’re referring to software here. There will never be a bug-free version of anything. Just look at Windows, Mac OS X, iOS, Android, your favorite browser, your favorite office software suite, etc.
A release is considered stable when it has gone through the (at least a month long) beta and release candidate cycle and all reported bugs are addressed. It’s then released as final, but now it’s being used by millions more and their variety of configurations, so of course more bugs will be found.
If you’re interested in being a part of this process, or at least following along, development on 4.3 is starting tomorrow (April 29) with an intended release goal of August 18: https://make.www.ads-software.com/core/2015/04/28/wordpress-4-3-kickoff/