Thanks AnonyMonk,

In this case, it definitely is related to data transmission over the wire. Arduino's Wire library's Wire.write() method sends the data back big endian. This confused me when I first ran into it, as my 2-byte word was backwards when I re-assembled the bytes.

What caused me further confusion, was that I kept relating endianness with what I've been learning for the past year dealing with hardware registers. For some reason, I wasn't correlating that we're dealing (usually) with *bytes* with endianness, not specifically bits as dealt with in hardware registers regarding LSB and MSB etc.

Little end first, big end first :)