Declaration of Apple:
We discovered a bug that prevents us from making apps with HealthKit available for iOS 8 today. We are working quickly to fix the bug in a software update and we will be able to release apps with HealthKit by the end of the month.
The company was even beginning to approve apps that make use of the new health API when a serious bug was detected which forced it to remove them from its store. Apparently, we will have an iOS 8.0.1 coming in the next 1-2 weeks (TNW)