Sammael, as I mentioned, I don't understand the economics. What I do understand is that I was at a panel, and a whole bunch of magazine editors and publishers said the same thing. Off-the-rack is better for them than subscriptions are. Especially if you didn't think you were going to have that many subscriptions and put the initial one-year subscription rate low enough that you'd be taking a loss on it. (I don't know if they did that, but I do know that magazines aren't expected to be profitable in their first year of publication, and there's a lot of "do this at a loss in order to build readership" at first.) If they got a lot more signups than they wanted, that little loss would get big.
But fundamentally, as I said, I don't know the particulars, and I don't know the economics. I just know what a bunch of magazine publishers said themselves, and was guessing that their "rack, not mailbox" mantra might have something to do with Amazing's situation, given that Amazing was having trouble getting onto bookshelves.