Valerie D'Orazio noticed that all DC's Vertigo titles had disappeared from the DC iPad app, which is powered by comiXology, although they remain available on comiXology's non-publisher-specific comiXology app. We wondered if this had something to do with the fact that the DC app is rated 12+ while the Comics app is 17+, and a quick e-mail to comiXology CEO David Steinberger confirmed that hunch:

Yes, the DC app is a 12+ age-rated app, while Comics by comiXology is a 17+ app. Vertigo title[s] purchased on our app or at comics.comixology.com will appear in the DC app, as long as you're logged in as the same comiXology user.

The Comics app is free, so as long as you're over 17, you can buy titles like The Losers, Fables and Sandman from the Comics app and read it in your DC app—a bit cumbersome, perhaps, but it works.

UPDATE: I e-mailed David some follow-up questions; here are his answers:

Brigid: So the key is really that if you have a comiXology account, your identity is constant across all the different apps?

David: Yes, every app (and the website comics.comixology.com), with the current exception of the Marvel app, is part of the comiXology platform, so if you buy DC on the DC app, you can view it on the Comics by comiXology app, or on comics.comixology.com, and vice versa. The same with BOOM!.

I feel like this hasn't gotten enough attention. We were the first to have digital comics available both on the iOS and on the web, so you don't even need an iPhone or iPad to buy and read digital comics, but if you do, you can buy and read on any of these devices and the web.

Brigid: Are you restructuring it so that all the apps appear to be 12+ unless you are logged in as an older user? Someone just said to me that the Boom app went from 17+ to 12+.

David: Nope, we just made the argument that the BOOM! content was 12+ and was mis-categorized as a 17+ app. Apple apparently agreed, and on the latest update let us move it to 12+.

We don't currently have parental controls built into the app, so whole apps have to be either 12+ or 17+ (or 9+ or all ages).