Google is known for periods of spring cleaning and now it has looked towards its own mobile application marketplace, Google Play, culling around 60,000 low-quality apps in February. Quite a large number of apps, considering that the store contains about 700,000 apps. Not all of the apps were deleted by Google though. Some may have been pulled by the publishers themselves, but a majority of these were most probably directly culled by Google.
Unlike Apple who vets apps prior to publication on the App Store, Google scans its app store after the apps have gone live. This sort of post-publication scanning has led to malware apps ending up on the store though its automated systems are constantly being improved.
If apps do get past the automated systems, Google Play has historically quickly deleted applications that violate its Terms of Service, such as those spreading malware, graphic or sexual material, or infringing on copyrights.
This information comes from sources in the mobile app industry who have spoken with TechCrunch. A large number of the culled apps included MP3/ringtone apps, usually from shady publishers. It seems Google Play has grown large enough for Mountain View to improve upon its automated algorithms to handle spam applications.