It does seem a little silly that people can upload images without a license tag. This functionality could easily be added - perhaps any upload without a tag selected from the drop down or an appropriate template in the summary should not be able to be uploaded.
at first that sounds like a nice idea but it has two problems.
1: very often for large groups of images from the same (particularlly PD) source a new tag is created both to save the uploader time and to provide a usefull sorting of such images. Any mechanism like this would put a lot of beuracry in the
2: we will most likely end up with a lot of people picking tags at random which is a much harder behaviour to deal with than people not tagging at all.