What you fail to understand is that when the volume knob was new, it WAS patented... and those who used it paid a royalty to the inventor of the volume knob, because he thought it up, not them. Perhaps, they had to use a volume slider instead.
Now, the volume knob IS obvious.
Did you know that Alexander Graham Bell (my great, great, great grandfather, incidentally) only beat Elisha Root to the patent office by a few hours with his application for the patent for the telephone... and that within a month over ten other working telephone patents were submitted to the patent office? It was an idea that was ripe... an idea who's time was ready, to personify it... so one could say it was "obvious," since twelve inventors were working on the basic idea, yet it was patentable... and my ancestor was granted the patent by being first in line. (Family lore says he may have also been the one who greased the palms the best!)
It's said that the only non-obvious invention was the phonograph. . . that no one else was working on anything similar when Thomas Edison pulled the idea out of a dream.
In this instance, no one thought of a way to implement the multi-touch gestures within a sub-window on a screen without affecting the entire window display (and that is REALLY what this invention is all about!) that worked before Apple did it on the iPhone. That means they get to patent their method, and control what's done with that technology for a time. Sure it's obvious now... but those who use it are going to have to pay the inventor (Apple) for the license to do it... if Apple will allow it to be licensed.
Gray was the inventor of the telephone... and may actually have beat Bell to the patent office...
I always thought Elisha should have called ahead.
I knew a guy who patented an improvement on a wheel-barrow handle. His handle made it easier to lift heavy loads. The guy discovered no one had ever patented the wheel-barrow itself. He filed for a patent, but they turned him down.