Well what if you want to make a historical scenario- right now you would have to assign a certain resource to a particular large wonder to make the Pyramids of Ghize exclusively Egyptian (and this works on a pre-made map only).
I think an option like the one I sugest is quite urgently needed for scenario makers etc- that want to keep wonders to their originals constructors and this way give historic bonuses to the actual people that really had these. Egypt was powerful in the times when they build these things- and not the celts (if they'd built them).
Besides there can still be non-civ-specific large wonders (internet, Cure of Cancer, and so on), but the posibility to make this flexible would be a great improvement over the current state.