Braun didn't make computers, or phones, or tablets.
If you made a computer mouse inspired by the shape of a Porsche 911 you probably wouldn't have any problems, but if you made a car modelled after a Porsche 911 you certainly would.
Apple hasn't argued that rectangular phones are it's exclusive domain, however it's case is characterised by some people. It's saying that the many, many similarities are so numerous and so dominate the design of some Samsung products that it believes some consumers would have to actually expend deliberate effort to tell those products apart from Apple products, and that this is going too far.
They're basically arguing that if there is a line that it's possible to cross when making your product look too similar to someone else's, then Samsung has crossed that line. You could disagree. You could think that there is a line and Samsung didn't cross it, or that there is no line and it's OK to completely duplicate another company's products so that yours are actually identical. Are you in either of those two camps? If so, which.
This also relates to the 'Poor artists copy, great artists steal' idea. The point isn't that great artists are better at making their stuff look like someone else's, or something. That's a popular misinterpretation. The point is that great artists take the idea and make it their own. They produce an expression of that idea that is so 'theirs' that they now own it artistically.