Here's the thing...
The point that the commenters here and elsewhere seem (to me) to be missing in all of this "My Grandma's Morris Minor thad round corners LONG before the iPhone, so THERE!" is that, once you get past functional design (You can't design an efficient airplane with both wings on the same side, for example) aesthetic design and trade dress are common ways that you differentiate your product from someone else's.
In the cellphone design space, there are a LOT of ways to make your product look DIFFERENT from someone else's and ONE way to make it look the SAME.
Looking at other cellphones, you can see that some are taller than the iPhone, or wider, or have visibly larger- or smaller-radius rounded corners, or concave or convex tops or sides, or trim/detailing placed here or there, or different styling to the interface (vis. WinPhones), or any number of ways to differentiate and make any particular product stand out.
...And then there are ones with essentially the same physical proportions, essentially the same diameter corner rounds, essentially the same detailing and styling, and essentially the same styling to the icons as used on, and identified in the public mind with, the iPhone.
In the one case, the manufacturer is trading on the reputation and appeal of its brand and its particular engineering and style to sell its product. In the other the manufacturer is trading on the reputation and appeal of another company's popularly-desired product, saying "You can get something that's JUST LIKE that but cheaper, from us!"
If Ford made a car that, except for the badge, was physically identical on the outside to a Mercedes or a Ferrari, you can bet that those makers would be taking Ford to court over it. That styling is what sets their products apart to the casual observer. If you turn to stare enviously as a Ferrari drives by, you are extrapolating everything that you identify with the concept of "Ferrari" -- power, speed, hot babes, and the money to afford all of them -- with the external appearance of that car going by. This is why companies defend their appearance and trade dress so vigorously.
From what I've read, Apple is not saying that all your round-cornered rectangle are belong to them -- they're saying that they will aggressively defend their designs from any efforts to make a similar product that is visually indistinguishable from theirs to the average observer.
I don't really see that as being unreasonable.