You're referring to the Distribution field in the Add/Edit Release section - honestly, I wouldn't worry too much about the details in there. This is something that was carried over for Machina from the "Pro" section, as his charting tools require understanding what is "Retail" and what is "Digital" - those drop-down options came from that part of the site.
You'll note the information isn't really displayed anywhere on the game page (other than if you come into this option, to edit) - so I would just say, unless you know for sure a game is a "Retail" distribution, I wouldn't even bother with the field (we're perfectly fine with having it left blank). If Machina needs it set to something specific, he may do so himself... :)
In that case, you might want to reduce the section to a simple "Retail: Yes/No/Unknown" choice then for users that don't need the extra functionality. It's really confusing the way it is right now, at least for PC games.