Yeah, they must have done those changes to optimize on some calculation loops (the extra microinstruction on on of the branch opcodes for example too)
FWIW here's another one with many changes over the standard instruction set. TMS1100 Touch N Tell: http://pastebin.com/7XRvyvt5 *edit* woops, that note for opcode 04 is a2aa, not a4aa.
