Just ahead of the WWDC keynote that kicks off tomorrow at 10 AM PDT in San Francisco, AppAdvice reports the App Store has passed 400,000 available iOS applications. According to data provided by App Store tracking system AppShopper, there are 401,446 iOS apps at the moment of writing this, though in three years Apple approved just over 500,000 apps – 507,293 to be exact. The important milestone of 400,000 apps (if AppShopper’s figure is to be trusted, but we believe so considering 148Apps reports 398,845 as of May 30, 2011) will surely be part of Steve Jobs’ keynote slides tomorrow as he explains why the App Store is a thriving marketplace for developers willing to monetize their efforts, in spite of the recent Lodsys controversy that, perhaps, will also be briefly addressed by Apple executives on stage for the purpose of clarification. Interestingly enough, however, AppShopper reports 97,946 iPad apps available whilst the App Store app on my iPad says there are 92,483 apps as of today.

The App Store officially launched on July 10, 2008, a day before the release of the iPhone 3G running iPhone OS 2.0.1. In 1060 days – or 34 months and 26 days as Wolfram Alpha calculates – the original App Store has been organized in two different sections in iTunes (iPhone and iPad apps) and a separate one living in its own application, the Mac App Store, launched on January 6, 2011.