After an outage spanning almost 24-hours, the Apple App Store is back on your iDevices. Apple users weren't able to view the App Store, update or download new apps to their handsets, unless they connected it to a computer during the outage. Now though, you should be once again able to access the App Store.
Interestingly, the App Store is once again asking users to download Apple's own apps via a pop-up message. Normally that's a one-off pop-up that appears when you first activate the App Store on your mobile device. Perhaps resetting that notification is how Apple achieved a fix?
Let us know if you're still having problems, otherwise, sing your songs of glee in the comments that you can now update Angry Birds.