I2C and SPI pins are matched accordingly in order to support I2C and SPI based shields: Nano V3 I2C bus pins (SDA on pin A4 and SCL on pin A5) are matched with Mega 2560 PRO pins (SDA on pin D20 and ...

It’s a significant update. The Arduino UNO and Arduino Mega 2560 update the Duemilanove and Mega respectively. They now use an ATMega8U2 instead of an FTDI USB to serial converter chip.