Regarding the requirement for all skins to include the jQuery registration:

The "Reusable DotNetNuke jQuery Plugins" page doesn't specifically say that these are requirements for skins (or modules). It appears to say that these are components that may be used for modules or skins if you choose. I am not using any jQuery in my skin or in any custom modules, so I wouldn't think it would be necessary for me to include it. Shouldn't the DNN system include what's necessary to make the builtin components function properly (such as the edit behavior)? If it is effectively required for all skins, why not just let DNN include it automatically without each skin having to include it? If it is a requirement for all skins, I think the documentation needs to be more clear about it.

The workaround I found of including some modules - those modules register jQuery because they themselves use it, which just coincidentally lets the editor function because it also requires it. 

It took too long to stumble across the workaround, and I was unable to find any documentation or forum posts that helped based on the error message, and it also took too long to get information on the actual root cause of the problem. Thank you Richard Howells for linking to the relevant documentation, and David Jamell for specifying how to fix the skin. There needs to be more official communication and documentation about this.

In looking further, it appears that we fail to include < script jsObject="DDRjQuery" / > in our DNNAdmin menudef.xml file.  This would force jQuery whenever the module action menu is displayed.