Update: We've since talked to Chip Mosher, Comixology's VP of Communications and Marketing, about the change. Here's what he had to say regarding the reason behind the removal of the digital storefront:
As for whether Marvel and DC apps will also have their digital storefronts removed -- both apps are powered by Comixology -- he said that "would be a better question for them." We've reached out to both Marvel and DC for a response.
"As we move to complete the acquisition with Amazon, we are shifting to the web-based purchasing model they've successfully used with the Kindle, which we expect will allow us to strike the best balance between prices, selection and customer experience.
There are many advantages to shopping at comiXology.com. Because of the content restrictions our mobile partners have, shopping on the web provides even greater selection of comic books and graphic novels. iOS customers will now be able to save money with comiXology's exclusive web-only Bundles, take advantage of Subscription features and enjoy eGift Cards. We also made our website more tablet/mobile friendly on all devices to make the purchasing process that much easier. And in Safari on iOS, customers can easily save a shortcut to our webstore with the "Add to Home Screen" feature.
In the new Android 3.6 upgrade we have a new comiXology in-app purchase system and a great new shopping cart, one of our most requested features. In the new app, customers may be prompted to update your payment information to continue purchasing books. This is a one-time action after which you can purchase inside the app."