Consider a system where an address consists of a segment identifier combined with a byte offset within the segment. The relationship between different segments is unspecified. Pointer equality has to consider both parts of the address, but "<", "<=", ">", and ">=" can ignore the segment identifier and compare only the offsets.

Given two distinct objects, x and y, (&x == &y) is meaningful, but (&x < &y) isn't particularly. (Except that sometimes it would be convenient to have a consistent total ordering on addresses, something that C doesn't define.)