[LAU] Rolling off high frequencies when mastering?

[Reuben Martin]

Yo, back on Tuesday 20 April 2010 Ken Restivo was all like:
> Kind of a general mastering question, but obligatory Linux screenshots of JAPA are included, I promise.
> 
> I've noticed with some professional cd's/oggs/mp3s I have, the high end is rolled off at around 20Khz.
> 

What makes you think that is due to mastering? Consider the fact that most mics freq response begins to roll off between 16k and 18k...

-Reuben