They don't have the same unsigned arithmetic.
That seems wrong to me. In fact it seem the wrong way around for me.
For signed binary arithmetic there are two option:
One-Complement: Where we have symmetric positive and negative ranges. Including a negative zero. Seldom used.
Two-Comlement: Where we have asymmetric positive and negative ranges. With the negative range having one extra number.
But for unsigned binary arithmetic I only know one way of doing it. 30 years of experience in the field. More then a dozen programming languages learned. Degree in computer science. I am hard pressed to even think of a different way to do unsigned binary arithmetic. Even on a purely abstract and academic level.
But one is never to old to learn something new and I a the curious type: Please enlighten me!