Hey Guys,
Apple takes 30% of all in-app purchases(anything bought with iTunes ID). This has been the case for Zinio since the update back August 1st 2011. So they just the same as all other apps(including the magazine ones in the newsstand) now share the revenue with Apple.
This was something they changed back in April and made mandatory going forward(they loved Zinio so much they gave em several months to implement the option in the app)
That being said, Apple will always taken 30% of all in-app purchases made with an Apple ID whether it's through Zinio or the publisher's app, it just so happens that they have made a newsstand folder for all the magazine apps that individual publishers make and now make it way more visible to customers so that they can reap that 30% from people who would buy the paper mag if they didn't know about the App.