Google’s Danny Sullivan stated that Google was not targeting low quality websites and confirmed there is nothing wrong to fix in sites that lose rankings. This is not targeting based on quality, but based on relevance. In other words, Google is doing their job.
Here is the text of Google’s announcement: “Each day, Google usually releases one or more changes designed to improve our results. Some are focused around specific improvements. Some are broad changes. Last week, we released a broad core algorithm update. We do these routinely several times per year….”