1 person being able to access data from every Apple account is certainly not in the realm of 'minor'. It's just thankful that the person that did it was a researcher, and not a hacking group, otherwise the dev center would still be online and Apple would be none the wiser.
Make no mistake, this was a BIG hack and a MASSIVE flaw. If someone had gained access to all that data, or even been able to get further into the system, it could have destroyed the online stores (AppStore, MacAppStore, iTunes Store, etc).
He only got names and addresses of developers. How could that have destroyed the iTunes store?