Yes, you guys have correctly assessed the situation.
The 10.1.1 SDK model for editing geodatabases utilizes Feature Services for maintaining geometry and attributes for simple features only.
Direct reading of datasources using WorkspaceInfo is very basic, and read-only at this time. Not many folks are trying to use dynamic layers like this. The API doesn't really support it.
In short, the API will continue to be improved to better support direct reading/querying of "ad-hoc" datasources that are added to the Map, free from the map package requirement, but this will still not be there for 10.2. It is on the radar for a future release, but very important for us to get done.
John, I would not say that your use case and current implementation is "fringe" at all, by any stretch. There are many requests for this kind of direct editing and access to GDB feature classes, and there are many current Engine apps all over the world doing this, as Esri has trained Engine/ArcObjects developers to do this. The Runtime SDKs and their editing frameworks are designed more for a simpler/streamlined editing model and experience, one that is not so granular, which eases things a lot, but does make migration from ArcObjects to Runtime sometimes difficult.
Marco, your comments are excellent. As you've stated, many more options are on the horizon.