Just a couple of things
iTunes does not use MP3 but AAC (Advanced Audio Codec) or m4a (mpeg4 audio) which is an evolution of MP3, but far superior in many ways.
I agree at high bit rates with AAC it requires an experienced listener with good source material and an good playback system to tell the difference. However one of the issues in listening to Non-lossless audio long term is the mental fatigue it can cause. This is particularly evident in cinema sound tracks for FX laden movies.
My significant listening experience has shown that what is acceptable on a middle range system, when played back through a quality system very quickly results in listener fatigue. So although the average listener may not be able to consciously tell the difference in A/B comparisons, this does not mean that there are no subconscious effects such as increased cognitive load due to having to re-create the missing sound information.