That last way to handling digital readership is rarely used by publishers who are very concerned about getting people to download and use their new apps.
One publisher, though, that is trying this approach is the U.K. trade journal InPublishing. The app description for InPublishing Magazine makes it very clear that the app ONLY (their caps) works if you are already registered with the publisher. Registration is free, but the new reader must complete the qualification questions to get in their system.
The reason this kind of app is called a 'reader' app is to differentiate it from a subscription app where the reader can sign up directly through the app. Apple doesn't allow for registrations directly through an app, one must either sell a subscription or else create a reader app.
Many other media apps have tried the reader approach such as Netflix, but eventually most decide to change their apps to allow for in-app purchases. The reason for this, or course, is that the goal is new paid users.
But many B2B publishers aren't after paid subscribers, they want qualified readers. So a 'reader app' approach has merits.
In the case of InPublishing, once the reader has signed into their accounts they can then access all the available issues free of charge – the magazine is a six-time a year publication.
Sadly, the digital issues here are replicas of the print edition – another example of the publishing trade being a behind the industry instead of leading it. But at least they have an app, something that can't be said for their U.S. counterparts.
(The magazine is also available for reading on the magazine's website through Flash flipbooks built by Yudu Media. No doubt Yudu is also responsible for the iPad app, as well – though I could find no vendor branding on the app itself.)