It's pretty tough to be all things to all people and still beat the competition to market in the first revision of a new product! There are plenty of feature requests that I can guarantee have many more votes in the Omni development database than probably any workgroup feature, like it or not. That's not to say they shouldn't address the issue of how to use it as anything but a solo practitioner, of course.
What do you want to accomplish with this system? As Omni has undoubtedly told you, if two different users change the same action (doesn't even have to be the same field) and then sync, one user's changes will be silently discarded. To stay clear of such mishaps, everyone has to stay in different parts of the pool, or have some out-of-band mechanism to make sure only one person edits at a time in a shared project, and a sync is done by the first writer before the second writer makes a change.
You could make a folder for each person where all of their projects live, with the understanding that one didn't change anything in someone else's folder without talking to them first. But again, we get back to the question of what the desired goal is -- this isn't going to work very well for a delegation scheme where one person is farming out work to the others, for example, because of the need to constantly coordinate who is allowed to make changes.
What gave you the impression that OmniFocus was intended as a multi-user environment? For most applications, that's really the exceptional case, not the usual one... I ask not to make you feel bad about your choice, but rather to see if there is something in the marketing materials that is misleading in this regard, because I know that Omni doesn't like unhappy customers, and delivering something other than what the customer has been led to expect is a surefire route to an unhappy customer!