It has to do with how it is encoded before being burned. I just tried to explain it without using super-big-ulous words, so someone else can give you that.
Your 'microphone' in your ears is not perfect. It is puny and way the way in there. It does not pick up all frequencies with equal preference. After some big math, people figured out that there is a big difference between frequency and wavelength when it comes to acoustics. If you lose precision where the ear won't care, you can do something awesome, like double the dynamic range or something.
This is just me making an educated guess though. I could not find specifications for different audio formats.
<quintopia> You're not crazy. you're the goddamn headprogrammingspock!
<Weeks> You're the goddamn headprogrammingspock!
<Cheese> I love you