That's interesting! Do you think this is because 64-bit code simply doesn't use a lot of its instruction set space (where more opcodes and instruction modes and variants are undefined and therefore not routinely used in executables), or because some of the people hand-writing 8-bit assembly actively use more opcodes than a typical compiler would, or some other factors?

Or are there are a lot of pointers in 64-bit code that contain a huge number of zeroes? :-)