I believe the main issue with their QA is that the same people who are working on the next expansion are also working on QA / fixes, at the same exact time, and since PDX pushes out content as fast as possible, the entire QA system is the least important to them.
This was fine when their games were simple and basic or outsourced, but games are becoming more and more complex, and their system of doing things simply doesn't work anymore.
Unfortunately, because PDX has recently become a publicly traded company, they now only care about profits, which means until their poor management starts becoming a serious cost issue, they wont be changing anything anytime soon.
So their games will just be getting worse and worse with quality.