Wish I'd Googled this question before just spending all that money on iWork.
I'd just assumed that iWork on the Mac would be integrated. Silly me.
I'd put off upgrading from '08 as there were no features that I wanted - then I decide that the killer feature is iCloud, and it's not there.
The one saving grace is that if you manually up/download documents with iCloud, then you do need iWork '09 for file format compatibility.
Now that I've spent the money I guess that iWork'11 will be out next week. That's what usually happens when I buy something.