For some reason, companies are afraid to embrace open source and free software. Whatever the reason, that's up to them. As a result, Comixology has comic reader apps for the iPhone and Android, but DC and Marvel and them only make their comics available on the iPhone.
Today, an announcement from DC. They've had fans demanding being able to read comics on the Android. Although he didn't say "Because you demanded it!" (although it would have fit), DC will now release their stuff on the Android.