Plugin Compatibility Tests
Our developers run extensive compatibility tests before releasing any update to our plugins and themes. With the large number of themes and plugins available in the WordPress community, we simply cannot test against everything.
This is why we and other developers, premium or not, request that users complete a conflict check. A conflict check is the fastest way to determine where the conflict resides thus allowing us to provide a solution as quick as possible.
Joost discusses this topic further in this article: The Honest Truth About Plugin Testing.
We do have an aggressive policy when it comes to plugin updating as when we encounter a bug we try to be quick with bug fixes.