Posted this in another thread but think this may be helpfull:
After hours of searching and testing many solutions people said to work for them to update (but didn't work for me), I managed to get all iWork apps in the app store and to update for free with these steps:
1. Install iWork'09 from CD/DVD if you don't have iWork installed
2. Update iWork'09 to version 9.3 manually (http://support.apple.com/kb/DL1563)
3. Change your system language to english in system preferences -> languages
4. Reboot and log in to guest account
5. Open the Mac App Store and log in
6. At this point you should be able to update directly from the featured page (or the app pages)
7. Install all updates, reboot and log in to your normal user account and change the language back to whatever you like
Your iWork apps should show in the list of your buyed apps
Hope this helps 🙂