Granted, for many content classes, that's true. For certain classes, however (most especially the built-in "folder" class), you almost always want to carry over the subtree. It would also be nice if you had the option of creating a true "copy" at the new location or just a "link".
I'd simply like to be able to maintain *any* content element at multiple locations without having to update multiple copies. It's neither intuitive nor particularly useful the way it works now.
There's no need to link in all subchildren to both locations. If you want a folder to show the same children in all locations you only need to change the template listing. Instead of fetching children from the current node you should fetch them from the main node of the object, if you then make sure that new subchildren are always placed at the main node you will not have any problems.
It is not a flaw but a design decision to not make things more complex than they need to be.
I can't see that you could get full functionality just with templates for carrying the subtree with you at the added location.
It will work fine at the first level when you open the object from the added location, the template could view a tree view or list view of the main locations children. But when you want to go deeper into the sub-tree you will then jump to the sub-tree at the original location.
If you ie. want a folder and its subtree to be viewed also at another section that has another design, then you should be able to let this object carry the whole subtree/all children into that added location.
Please consider making this feature in a future eZ publish-version :-)