In an ideal world, maybe
Oh come on - is this the first time that an OS upgrade has borked applications that worked fine in the previous version? No - and it's not an Apple-specific issue, either. It's an upgrade in the same sense that WinVista > Win7 is an upgrade - it's a substantial OS revision, and not something to be undertaken lightly.
Yes, Apple should admit that there are possible issues with in-place upgrades. They should probably also admit that there are profitable side-effects of not allowing users to replace their laptop batteries, or from making people pay £20+ a go for an adapter that lets them connect their FruitMachine to a non-FruitMachine display. They should probably also admit that occasionally the concepts that they implement with a very nice UI have already been implemented elsewhere beforehand.
Apple have very savvy marketing people. Do you really think they're going to sour their release-date marketing buzz by saying "careful now, some software might not work with the new version", when they can instead rightly point out that it's the user's job to ensure all their stuff will work with the new OS?
It has long been a very very obvious fact that, prior to a major OS change such as an upgrade, you should check that *anything* you depend upon for work or leisure purposes will be completely compatible with the new OS. Apple could do more to spread awareness of this, but it's still the user's own fault if they upgrade without thinking first.
Tl,dr; - No matter what the marketing droid claims, it's not a fucking magic box. Stop expecting it to behave like one.