This isn't clarification, it's changing the intention based on feedback. I really don't see how "…commissions for all app and in-app content will be reduced from 7% to 2.5% globally," could possibly mean "only in app purchase commissions will be reduced." Sounds like straight up double speak to me, and I'm not sure what they lose in just being honest.
They announced their intention to change their affiliates program. People and organizations who relied on that program were not happy about it and voiced their concerns. Now Apple has changed their minds about what the scope of the change will be. This can easily be played as a community-friendly move, and it seems to me like it would be a big PR win to do so.