For those of you that haven't upgraded to iOS 8 yet and still experiencing this issue the following was posted over on Reddit.com today:
Easy fix for not being able to update apps through AppStore. (self.jailbreak)There's more information in the comments just in case you may need more assistance.
Resolution: Switch your system language, then change it back. Should restore functionality.
- If you have issues where Update button opens the app.
- If after syncing through iTunes still shows updates available and icon switches between Update ---> Open.
Not working for me.