The app ecosystem surrounding Apple and its products has "become an economy in and of itself," Apple CEO Tim Cook said Monday in his WWDC keynote speech.

To prove the point, he rattled off a series of stats to show how big that ecosystem has become--particularly as it pertains to iOS products:

• There are now 400 million customer accounts on the iOS App Store.

• More than 650,000 apps are available in the store--and 225,000 of those are made specifically for the iPad. Competing tablets, Cook said, only have a "few hundred" apps available for purchase.

• App Store customers have downloaded 30 billion apps.

• Apple has written checks for over $5 billion to developers--and that's after taking its 30 percent cut of all App Store sales.

• The ecosystem will get larger: The App Store is available in 120 countries, but that number will grow over the next month to 155 countries total.

"Despite these blowaway numbers, what we do together is much more important than any set of numbers could ever reflect," Cook told the audience. "For Apple, and for, I expect, many of you, our goal has always been to do great work."

WWDC itself is sporting some impressive numbers, Cook said: Attendees came from more than 60 countries to attend the conference's 112 sessions and 125 labs.