During the work on the http://wiki.magnolia-cms.com/display/DEV/Concept+-+Multi-item+Actions for 5.1 release, the issue with different delete command for asset and folder has jumped out in the DAM module.
In general, the problem is that a different action/command is called for different node type, although doing basically the same thing (at least from the user's point of view) - in this case marking the asset/folder for deletion.
The problem has been "solved" by not including the "Delete items" action/button into the actionbar section for the multiple node types. But this is not ideal solution from the user's point of view, as in all the other apps the user can delete multiple items, even of different type (e.g. folders and contacts in the Contacts app, content nodes and properties in the Configuration app, etc.).
The solution would be providing a "decision-making" action, that could be configured to call different "sub-action" for different node types.