The Next Web received the following statement from Apple:

We discovered a bug that prevents us from making HealthKit apps available on iOS 8 today. We’re working quickly to have the bug fixed in a software update and have HealthKit apps available by the end of the month.

HealthKit is a major new feature in iOS 8. I hope they get this fixed before everyone relegates the Health app to the “Default” folder on their last home screen.

(Via Daring Fireball.)