As the digital marketplace continues to grow and evolve, it seems that some folks can't (or won't) grasp the distinction between digital and physical media. Thus you have HarperCollins trying to sell libraries on ebooks that expire after 26 checkouts (because ebooks don't wear out like physical books do), numerous publishers who think they can put regional restrictions on ebooks, and the Marvel Digital "vault."
Last year, Marvel sent out a newsletter saying that Daredevil #1 and The Invaders #1 were going "into the app vault" on a certain date. This mimics Disney's strategy of making its DVDs unavailable for long stretches of time, to encourage people to buy them before they disappear. Disney basically creates artificial scarcity to drive sales, which is kind of obnoxious from the customer's point of view. With digital comics, it seems downright perverse. As David Brothers cogently explained at Comics Alliance, it tries to carry over the physical concept of scarcity into the digital world. At the time (last November), he urged fans to speak up.
Either they did so or someone at Marvel came to their senses, because the Wall Street Journal reported last month that Marvel seems to have abandoned the digital comics vault; an unidentified spokesman told WSJ reporter Eric Felten that "Marvel is not implementing a vault strategy at this time for its Marvel Comics app." Admittedly, they weren't pushing the idea that hard—aside from the newsletter, there was no press release, and no one at Marvel wanted to talk to Brothers about it at the time.
Still, that doesn't mean the vault is blown up. The comiXology and Comics+ apps carry both comics, and Graphicly has the Invaders but not the Daredevil one. The only app I couldn't find them on is the Marvel app. Maybe they have a mini-vault for just that app? Both comics are available through the Marvel Digital Comics online service as well. Which points to another problem with Marvel: Too many digital platforms, not enough integration between them. But that's another post.