I used to use MP3 players that required (or supported) drag and drop... but once I began using some sort of music library (i.e., Zune, iTunes, etc.) to manage my device... I don't think I'd ever go back to a drag/drop method.
It's not easier. What could be easier then plugging up your device and having it automatically sync your new music, videos, pics, etc. based on your initial configuration (from device --> computer and vice versa)?
It's not faster. Having to open up the directory on the device, then open the directory of your music/files. Or you could use an app to automatically sync two folders, which you would have to launch, click on start, etc. etc.
For example, when I connect my WP7 device, Zune automatically launches, syncs new music between both my phone and computer. It excludes tracks that I've marked as "don't like" and it only syncs the videos and pictures folders that I've selected. It also updates play counts, etc.
In any case, as action jackson said, it currently does not support a "disk mode" and we're not sure when/if that will come to be. So... I would ask, why do you NOT like using the Zune software to manage the media on your device?
EDIT: Not to mention the wireless sync capability. Most days I don't even connect it to my computer... my phone is charging next to my bed overnight.... In the morning I turn on my PC in the living room and 5 minutes later, they're syncing wirelessly.