Based on what we knew, I don't find that assumption very reasonable.
"What we knew" is what was linked from rumor sites. The average user isn't aware of that info and shouldn't have to snoop around just to find out about things like missing features and no backwards compatibility.
I'm struggling to think of any software update/upgrade that wasn't or isn't backwards compatible at launch. Maybe someone can shed some light on that. What Program has been updated that will not load a previous versions data
This.
And the "it's a totally different" app excuse doesn't fly. If it IS a totally different app, apple needs to tell users that since upgrading an app you're already using is a completely different experience than dumping the app you were using for something totally new. Especially since if it's a clean slate, might as well consider switching to another app (since that's what you're essentially doing anyway).
When people buy an app with the same name but a different version number, they expect an update to that same app, not a totally different one. And that includes opening old sessions.