Interesting that they haven't allowed folks with the apps already installed from iLife to upgrade via the Mac App store.
It's a different system, and they were very clear that MAS can't mix with non/pre MAS
Which is why I suspect in the coming months they will stop preinstalling iLife. You might still get it free but via getting a download code to use in the store, just as they will do the free upgrades to lion for recent computer buyers