ArcGIS Online currently generalizes a hosted feature service if editing capability is disabled on the service. This is not always useful, and the only way to show the "true" service is to either:
a) enable editing on the service (which is not sensible as administrators do not always want everyone to be able to edit the service)
b) open the Feature Service using the "add layer to new map with editing enabled" (which is only applicable for users with admin permissions)
Please may an option be made available when publishing a hosted service to ArcGIS online to select whether the feature service should be generalized or not. This is already available when adding a shapefile to ArcGIS Online, and would allow admins to control the use of this functionality without compromising the integrity of their data.