iWork '08 was released for OS 10.4 originally from 2007. Whilst it would have free upgrades within its cycle e.g. 8.1, .2, .3 effectively this does not mean you get a free upgrade to a significantly new version 3 years later e.g. iWork 09.
In your case, its likely there was a temporary offer for a free upgrade initially to encourage customers to port to the Apple Store (for software download) rather than traditional disc installation. After a period Apple withdraw software these upgrades.
In terms of your re-install, have you signed in with the same Apple Store account used previously? If you haven't, it wont recognise your previous status and upgrades may be un-available. This is true of the 10.8 OS update - if it is on your Apple Store account as installed previously, you can download it again, if you come into the Store clean, you wont even see it as a download.