I am really disappointed by this. These days, I mostly use my (fifth) Kindle when flying on aircraft, and there I mostly read The Economist or The Atlantic. They don't publish offline media for laptops. I don't own a tablet. My phone battery is precious on trips. I guess I'll just look for paper copies at the terminal again...?
The conclusion to draw is that you clearly don't own your ereader either.
I mean DRM does not stop those unwilling to pay. If the only achievement of DRM is to annoy the people who are willing to pay, i wonder if it likely increases rather than reduces piracy. There is no reason why you shouldn't be able to be served an open epub with your magazine subscription.