"Rectangles with rounded corners are everywhere! Just look around this room! And look outside, there's even more, practically everywhere you look!" —Steve Jobs, 1981
> NB: rounded corners was itself a copy of the webOS viewport system.
Rounded corners have been a part of Apple's design for the entirety of the Mac's life. Only "recently" in Mac OS X has the Finder not had rounded corners. Those widget apps, such as Calculator, also had rounded corners way back when.
That said, it does seem very similar to WebOS's beautiful design. But who's borrowed from who? And does it really matter?
NB: rounded corners was itself a copy of the webOS viewport system.