If a designer signs a "work for hire" contract, then anything created under that contract belong to the client, not the designer, true. It's one of the main reasons designers refuse "work for hire" terms. [Another being that usually the WFH language usually explicitly denies me the right to use MY designs in MY OWN portfolio...uh, no thanks.]
Under non "work for hire" terms, if you hire me to design it, I'm only contractually bound to give you the finished work. All IP remains with me, the designer, until you pay me for the IP.
You might find it an "interesting" business model, but it protects the interests of those who use their creative skills to make clients money (in this case a /buttload/ of money). I never sign my IP away unless clients are willing to compensate me for it, and I never, ever, EVER sign contracts with WFH terms. Why should I?