“So what I wonder is, what’s changed in the world to make Marvel think that they can make this sort of product successful now? ”

Simply: bandwidth. You couldn’t get people interested in downloading over 28k or less. Even 56k was a struggle for large graphics. I once bought a digital comic years ago, but it was too expensive and too disappointing to buy another. There’s also the sense of collecting. You can’t really collect digital comics. And even now the price point on digital versions versus hard copy ought to be cheaper, since the user is providing the delivery and storage, but they aren’t. Which is stupid. More people will be willing to take a risk on a digital comic if it were cheaper.