this is totally off of one experience with burned cd's and an xbox:
my brother has an xbox from a little over a year ago, and when you try to put in burned cds, it does not read. he has a phillips dvd-rom.
my cousin just got an xbox for christmas this year, and when he puts in burnt cds, it reads. he has a samsung dvd-rom.
i am assuming it has to do with the dvd-rom drive and not that the xbox can tell if the cd is burnt or not.