The reality is that CD's used to be mastered to produce a "sound stage" - because the target was the hifi in people's homes.

Now the target is iPods, Cars and maybe Radios. So they mix to make it sound good in those scenarios (well, in lots of cases).

Also, whilst this sounds interesting, knowing more about the experiment might help. AAC compression can do more than just compress the music (might be doing some other form of levelling, and/or adding punchiness in some other form).