[AlexUA]

It might be a poor measurement of quality in general, but in Drupal's case it speaks to the growing pains Drupal core (and Core development in particular) is going through right now. Sun's post is specifically about new and untested/unproven UI modules that were forced into Core by Dries, that have added to the burdon for Core developers, as well as the increasingly complex (and very often poorly documented) Core code base that is making it very hard (or impossible) for new Core developers to get going.

One key thing to keep in mind here with regards to Drupal is the release cycle for Core. The current release (7.x) took three years to come out, so when things get shoved into Core it takes a looooong time to take them out, or even to improve their underlying APIs. This is as opposed to Contributed Modules (Contrib), which is where much of the power of Drupal is, and which evolves at a much faster rate than core (for example- Views went from 1.x-2.x-3.x in the time it took to develop Drupal 7).