Truth be told, the desktop is already a kind of weird folder that is obstructed by all other windows, so I wouldn't really care about those types of inconsistencies. So for the first case, I wouldn't mind if closing the last finder window would jump to the next app in the tabbing order as if I quit it. The second case is a bit more tricky, but I think it's should be a matter of focusing only if I click on the desktop specifically and not in any other case, eg tabbing or closing other windows.
1) If you had a single Finder window open, then closed it, focus would get stolen by whatever other application happened to have a window open.
2) There would be no way to use the keyboard to interact with an item on the desktop without first closing or hiding every running application.