Comixology didn't have much of a choice.
My major apprehension regarding digital comics was that we didn't own a copy of the file that could be backed up or whatever, like an MP3 file for music.
This is now addressed - at least partially, till DC and Marvel allow for it as well.
I'm not sure if it is a coincidence, but Apple is promoting 'Madefire' as an Editors' Pick. One of the things Madefire is publicising is that it allows for in-app purchase of...