When you get down to it, copyright is a whole bunch of contradictory rules. Courts decide every time there is a new kind of work, whether it is copyrightable or not. Trying to divine whether something is copyrightable by analogy to other kinds of works is a hopeless endeavour.
That was the case with computer software when it first became interesting to copyright. After all, it's just a series of instructions which are often not considered copyrightable. But, in general, copyright has carried over fairly naturally from the printed word to new types of media as technology advanced.
