Making the use of the button optional is a good idea, because it changes (relative) position if one rotates the device. But eliminating the button completely does not make sense, because it is useful for beginners. Gruber has more arguments in favor of keeping the button:
How in the world would you get home on an iPhone using a five-finger pinch while holding it one hand? The iPad seems like a “maybe”, but I find it really hard to imagine a Home-button-less iPhone. And even with the iPad, what about people who don’t have five fingers on one hand? No iPad for them? The iPad is very popular with impaired users. What about taking screenshots?