Have you tried this? I'm not 100% certain that the old version would be available in the App Store, even to pre-Mavericks users. Assuming it is, I'd assume you'd have to pay for it. If you'd already bought iWork, that would be a drag. In any case, it's a workaround, potentially costly and time-consuming besides, and not a place we should be as Mac users.
Yes I have tried it. My history is that a Mavericks system's update saw I had a copy of iWork '09 (DVD distributed) and added ownership to the apps in the App store. From that point I was able to download the '09 versions on a Mountain Lion system. Earlier systems might cause a problem (I didn't have any to test) since iWorks has been updated every year to the new OSes.
Agreed this is a PITA, but maintaining software backups is a necessity. I was burned a couple years ago when the iMovie I bought under Snow Leopard became unavailable six months later when Lion came out and the newer version was not backwards compatible. Apple support basically said "tough luck" but it is my understanding that they now maintain older versions just for such circumstances.
Why anyone persists in excusing Apple for this mess is a mystery to me.
I certainly don't! Because the "upgrade" is basically forced and the new version is used by default, I consider this a far worse deed than the Final Cut Pro and iMovie "upgrade" disasters in years past.
I turned off the update notifications, so at least I don't get pestered daily about the updates from the Message Center. I still see the "3" bubble from the App Store in my Dock but I can ignore that. Onwards we go, into the darkness...
But the problem with this is that you don't get updates for other programs unless you carefully select the ones to install.
Other apps, just not these, you can tell the App Store to ignore the updates.