I've never seen a game that allows Athas.org material...
you have not been looking hard enough; all of my games, online or in person, allow all wotc recognized official material, which includes all the designated official websites and the various publications.
as do several games i participate in as a player.
while we may disagree as to what we want to bother to include in a particular project / thread, what is official is pretty cut and dry. i have a thread attempting to detail it around here somewhere, which has gotten bogged down with time constraints and the sheer mass of what is actually considered official. =P
*edit: i should think that wotc's definition of official is the only one that counts or matters, regardless of whom else may be asked, or might have an opinion.