Quality means many things... When it comes to the experience of the people using the site, performance - how long it takes the requested page to display - is critical; the vast majority of Stack Overflow's page requests are someone requesting a page that they urgently need to read.

That doesn't preclude other aspects of quality of course. But it does influence how they're approached. A heavily abstracted system that hurts performance is unacceptable, but there are other ways to achieve the same ends.

You might find this article interesting... http://samsaffron.com/archive/2011/03/30/How+I+learned+to+st...

Yes, I know performance can be critical for some products - and that's the case for Stack Overflow. But I think you can't simply ignore other aspects like maintainability or security.

This article from Sam Saffron is very interesting. He was very reasonable testing the ORMs available, and only after realizing that none reached the performance he needed, he decided to write his own. The problem is when people do that and "reinvent the wheel" without searching if someone already solved that problem for you.

It's probably difficult to convey the scope of Stack Overflow's development in the span of a talk; I strongly encourage you to read the blogs of past and current developers, as they often go into far more detail about the concerns involved and the extreme care taken. The architecture itself is interesting, but IMHO it pales in comparison to the process that created it.