.ePUB extension should be reserved for non-DRM eBooks
I believe that Adobe should not use the ePUB extension for eBooks that have DRM applied. They can do what they want with PDF but ePUB is not their format and they have no right to take it over with ADE based DRM. They should develop a new extension for use on DRM'd books. The end user can easily be confused and not be able to read what they purchased. Only a very few devices actually support DRM on ePUB but many devices have support for ePUB.
For example Sony is careful to use LRF and LRX to distinguish non-DRM from DRM ebooks. Others should take this lead and adopt it as well. Several others also adopt this rule.
I think the ePUB committee should outlaw the use of the ePUB extension for DRM'd eBooks. Their extension has been hijacked for commercial purposes IMHO.