Thank you; I was confused then. Makes more sense to me now. Apologies for the contretemps.
However, one more question: does the Migration process truly leave out all the old frameworks when it moves your data and preferences and applications (if you are moving any)? I still think that having that old data could cause confusion if it gets brought into the new OS. But if it is being left out, then it's a non-issue.
[edit] I guess a better way to put that is does SL know to ignore old frameworks?
No worries.
Migration will move frameworks at the local level /Library, and the user level (if any) ~/Library that support the Applications that are being migrated. It moves these because they are needed for that Application to work. It is possible that it will not be compatible, but again that just means the application needs to be updated.
Old data can cause problems, I was never denying that. But the question is what old data? It can very well be Apple plists, which should simply not be the case. My only point is that it is not necessarily 3rd party data, some problems will simply be a problem with OS X. Which is fine, but blaming the user for upgrading when that is the only real option Apple is giving you is not fair at all.
Edit addressing your edit. Snow Leopard knows some apps won't work, hence that KB I linked. The frameworks that the application uses can be left, because Apple has already move that application into an incompatible software folder. Once you update, if the framework was the problem, it will be replaced with a new version of that framework that is compatible.
Of course Apple can't focus on every application. But there is more going on than simply frameworks. But there will never be old Apple frameworks in /System when you do an upgrade. I can guarantee that.