Except that Steve's quote is a good argument for the conservative interpretation, which says that if you don't use an iOS app as advertisement for non-App Store payment, nothing changes. Because to me it seems like there's no necessary IAP option implied and if the publisher isn't using Apple's means (including the iOS platform itself), it keeps its 100%.

That battle of interpretations rages on, unless I've heard different. It looks like Marco is taking the liberal interpretation (apps must accept IAP as a form of payment for any services they offer).

It seems to me this is the underlying debate.