iWork '09 is NOT deleted when you update - in other words, you get to keep both versions (old and new). So what's the problem exactly?
Maybe, the problem is that is stupid to launch a new version of an app that is way worse than the old one?
And, you know?, I'm sure that, in not too much time, old versions are going to have compatibility problems with new system versions.
So, I rather pay for a real upgrade than a crap DOWNgrade for free