Apple might not have trumpeted that over 100,000 applications are now available for its iPad tablets, but the company is publicly marking another milestone: customers have downloaded more than 15 billion apps from the App Store, and Apple has paid over $2.5 billion to app developers.

“In just three years, the revolutionary App Store has grown to become the most exciting and successful software marketplace the world has ever seen,” said Apple senior VP of worldwide marketing Philip Schiller, in a statement.

Apple launched the App Store back in 2008; since then, the company has launched the store in some 90 countries. Over 425,000 apps are available—more than 100,000 designed for the iPad tablet—spanning 20 broad categories. Apple says that, to date, there are more than 200 million iOS devices in use around the world.

Apple’s App Store was the first of its kind when it launched—despite the initial popularity of the iPhone, not all industry watchers were sure Apple could foster a developer ecosystem to drive the iOS platform. Although the company’s “curated” approach to offerings and ever-opaque app approval processes have rankled some developers, Apple’s App Store continues to set the standard against which all others are measured. And these days there are no lack of competitors, ranging from the freewheeling Android Market to Amazon’s own Appstore to specialized app stores for other mobile platforms like webOS, BlackBerry, Windows Phone, and even Symbian.