After you've closed all current documents, the close button doesn't work? Or do you mean that you expect Gimp to exit when you don't have an open document, even though you could still want to create a new one after closing the old ones? If that's the case, it'd be rather silly in the other direction, don't you think? If you wanted to create a new document, you would have to make sure you didn't close what you were done with first, because that'd mean waiting for Gimp to load back up again.
After you've closed all current documents, the close button doesn't work? Or do you mean that you expect Gimp to exit when you don't have an open document, even though you could still want to create a new one after closing the old ones? If that's the case, it'd be rather silly in the other direction, don't you think? If you wanted to create a new document, you would have to make sure you didn't close what you were done with first, because that'd mean waiting for Gimp to load back up again.