Here's what I did:
Rip a track from a CD using ALAC (Apple Lossless). Get a .m4a file
Rip the same track from the same CD using AIFF. Get a .aiff file.
Compare the bit rate of the two files (⌘ + I on iTunes or afinfo from the command line).
The AIFF's bit rate is higher than the ALAC's... Why? How can a losslessly compressed audio file have a smaller bitrate than its losslessy uncompressed counterpart?