I think the 8+ is when the exta 'features' start to kick in. Apple has an online manual of sorts. For each feature that it deigns to describe there will be a footnote saying which models include the feature. 7 is usually at the bottom of the list. That's not a good sign.
The one feature I'd like to have is where you can blackout any misc. crapola. Yes, I know that's not the technical term.
