inspriration is a funny word here. Most artists learn the rudiments of the craft, as has been mentioned in this thread already I believe, by exactly copying other artists works. They'd project images on walls using candles and pinhole silks to trace things perfectly etc.
To me, it feels like you are looking for a black and white line to draw regarding borrowing/inspiration/plagiarism, and not only do I think there can be no such line, I think the desire to have this line, is an interesting product of our times. What I mean is, we simply want to punish those who steal, and praise those who lead. I don't need the government's help to do that for me.
Plus, the sad fact is that if you allow corporations to own these ideas, all that will happen is whats happened in every other media: Ill hire you to design for my corporation, and since you are a struggling artist, you will give me all the rights to your work in exchange for a small salary, and now because I am wealthy and you are not, I will own your ideas, which is even better than me copying them and much cheaper. Oh, and you think my ficticious company must hire only the greatest minds in fashion to succeed and this will force my corporation to pay you even close to what you think you are worth, then I'd ask you to look at movies. Clearly (insert sarcastic tone) only the best and brightest actors & directors are at work these days, same with Music! Even if talented people were actually hired, how many signed bands own the music they wrote?
Copyright laws hurt artists, stunt innovation (how many types of jeans are there? how many would there be if levi's had pattented denim?), and in the end will suffocate a capitalist society.
My background is in computers. When I first got on the internet it was in '89. the web, dot.com's, etc didnt exist yet. There were hundreds of thousands of users daily, not billions or whatever it is now. My point is that there was innovation almost daily back then, new things came out so fast (gopher, cmcu, icq, etc), it was really an incredibly happy and exciting time. Then corporations came in and halted nearly all of that, and the innovations started to trickle out seasonally in very planned and marketed ways. In my mind, this happened as a result of a small group of people taking the reins of something and controlling it. Which to me is bad.
Perhaps clothing hasn't been visited by the copyright faeries yet, because they are too busy patenting the world's food supply:
http://members.tripod.com/nvikas/genetic-exchg.html