A couple of points from the Devil's Advocate department:
1. I don't know how it is at for-profit magazines, but at
Poets & Writers we have to maintain a certain editorial-to-advertising ratio.
2. Magazines are really expensive to produce. Print magazines are also at the mercy of an extremely limited number of distributors.
3. Most print magazines, despite the advertising, need the subscriber to stay for almost two full years to make a profit on the subscription. That's why renewal mailings can be relentless at times.
4. An argument can be made that digital magazines are actually value-added, based on convenience and depending on the customer's views on trees.
5. eInk versions (on the Kindle, anyway. We haven't managed to get into the nook publishing stream yet) don't allow ads.
6. I can't speak to Zinio. We use Texterity/Coverleaf for our digital version in that market. When I write "that market" I refer to audited electronic distribution streams that count toward the circulation figures necessary to set advertising rates. (It looks awesome on Droids and iPhones, btw.)
7. Kindle magazines (and, I believe, nook magazines) are not audited, do not count toward circulation figures, and do not share subscriber information with the publisher. Those are valuable things that the publisher is giving up.