Okay looks like the part numbers are actually different:
http://www.realoem.com/bmw/enUS/show...diagId=24_1132
http://www.realoem.com/bmw/enUS/show...diagId=24_1330
228i
24008638283
GA8HP45 - ZBS
M235i
24008645366
GA8HP45- ZB5
Could just be gear ratios are different without any other enhancements, not sure.