Pfft, trust Microsoft to push nonportable code.
Drop this into your address bar: javascript:var%20x=100;alert("x="+x+"\nx-1="+(~-x)+"\nx+1="+(-~x));
Raymond should've saved it for the next April Fools' Day.
Consider the last time you used a machine with big endian, non-8-bit-bytes, and something other than 2's complement integer representation...
At the time of the C standard, architectures were far more diverse; for better or worse, most of the more esoteric ones seem to have died off, leaving us with the ones that do happen to share many characteristics with a VAX.
However, all of those still use 2's-complement integers. According to Wikipedia a few existing mainframes use 1's complement (CDC 3000/6000, UNIVAC 1100/2200).
I know the standard allows different bit representations, but practically speaking, today you're almost never going to find anything other than 2's complement integers and IEEE floating-point; and if you do happen to be working on one of those rare and unusual machines that don't, I think it'd be the least of your worries... even Linus says he doesn't care about Linux running on non-two's-complement or odd byte-size machines.