Using ArcGIS Server it is possible to publish a map service, which has a URL like http://services.arcgisonline.com/ArcGIS/rest/services/Demographics/USA_1990-2000_Population_Change/MapServer/1
In this case, the "1" refers to the particular polygon layer. It's possible to create a featureLayer from this REST endpoint.
When I publish a map to ArcGIS.com the options are "Feature Access" or "Tiled Mapping". This means that the REST endpoint has /FeatureServer/ rather than /MapServer/ in the URL.
Am I correct in the assumption that ArcGIS.com doesn't support dynamic map services, and only supports feature services and tiled services?