Interestingly, a lot of the deleted apps are related to MP3s or ringtones. Google has several official reasons for deleting apps from Google Play, but it seems that this swipe is not about malware, copyrights or sexual material. Instead, spam and low quality of the apps have forced them out of the store.
Google’s Play Store is a place where every registered developer can freely sell apps. There is no reviewal process prior to publication. However, Google has quickly jumped in to remove the rare occasion when apps with malware make it through the automated filters. Apple in contrast does not rely on automatic tools, but has a small army of reviewers that approve applications before they land in the App Store.
Google and Apple have the largest app catalogs with Apple still leading in terms of quantity with around 800 000 apps. Google is close behind, but we don’t know the exact number of apps on Google Play right now. Google last confirmed it has 700 000 apps on Play as of October 2012.
source: Tech Crunch