If you are burning a Red Book CD, the audio has to be 16bit 44.1kHz LPCM. So if your CDs are playing in a normal CD player they are LPCM.
The AIFF format is a container format. The audio can be different sample rates, bit depths, LPCM or compressed (for AIFF-C). However, the audio doesn't have to be compressed to be saved as AIFF-C; the compression flag can be set to NONE. I assume iTunes is simply using AIFF-C format for anything AIFF.
EDIT: Post crossed with SteveS1