I believe that the MINI is a drop in replacement for the Basic Stamp. the premier platform of the day when the Arduino came to be.
the UNO, NANO and Mini, all use the same basic Atmel 328
the MINI pins for I2c are often NOT in the normal DIP rows, but either located off-center behind two pins in the middle of the board, or brought out to the end of the board.
AFAIK, all the UNO and UNO clones use the exact same pintout for the basic pins. some add a second location for ease of use.
the Nano and Mini use a SMT chip, not the DIP version and there are 2 additional analog pins available.
the NANO does a pretty good job mimicking the general pin sequence of the UNO making shrinkafying a bit easier.
the NANO offers A6 and A7 as standard pins.
the clones take a horrible amount of leeway on the MINI in regards pin locations.