Apple on Wednesday confirmed that the App Store now has more than 100,000 applications available for download for the iPhone and iPod touch.Apple senior VP of worldwide product marketing Philip Schiller called the milestone “a major differentiator for millions of iPhone and iPod touch customers around the world.”

The App Store reaches customers in 77 countries, according to Apple. Since its inception, the App Store has provided more than 2 billion downloads – Apple bills it as “the world’s most popular applications store.”

Apple has divided the content in the App Store into 20 different categories. Games remain the most popular single category, while there are also many apps for business, news, sports, health, reference, and travel, along with other categories.

Developers who wish to create applications for the App Store need a Macintosh and pay Apple a nominal fee for access to a Software Development Kit (SDK) which enables them to write code and test for iPhone OS. Once it’s submitted and approved, the application is available for general purpose and download. Apple keeps 30 percent of the price of the app, and the rest is returned the developer.

The rapid increase of applications on the App Store has caused growing pains, though. Some developers complain that it’s too difficult to get visibility for applications unless they make it on to a top selling list or appear in an Apple television advertisement; there’s also been a downward spiral of pricing that’s led to a lot of 99-cent or free applications. Still, some developers are still making quite a bit of money. Jeff Smith of Smule, makers of the popular “I Am T-Pain” application, noted that the app garners 10,000 downloads a day worldwide.