Some product managers spend more time designing products than they should. If you're drawing screen samples and logic flow, you're not writing requirements, you're specifying design. Check out On Reqs and Specs to understand the difference. Product design is a skill! Hardware is designed by an industrial designer. Why isn't software?
One such designer comments: Occasionally, some poor fellow at a dinner party makes the unfortunate mistake of asking what I do for a living. My initial (and quite subdued) response is that I help design software for artists. Then comes the inevitable question, "Oh, so you are a programmer?" A gleam appears in my eye and I no longer feel obligated to blather on about the rainy weather. With a great flourish, I whip out my gold nibbed pen and draw a little diagram on a napkin that explains concisely how modern software development works. In the grand finale, I circle one of the little scribbles buried deep in the entire convoluted process and proudly proclaim "And that is what I do!" This admittedly selfish exercise usually keeps everyone involved merrily entertained until dessert arrives. Read more about software design in.