Gez said:Well, it could be construed as false advertising.
The balance of the two games are widely different, making this compatibility harduous.
"compatible" comes in degrees. I think the whole "permission to make products using the D20 System" "advantage" to the WotC OGL/D20SRD/D20STL is silly, because i've long considered most RPG books "compatible" in the sense that i can take any two RPG books i have that i've read and use material from them together without having to spend any significant amount of time meshing them. Moreover, the amount of time it takes me to mesh two products for different game systems is no greater than that for products fr the same game system, provided the latter aren't explicitly designed to work together [so this argument doesn't apply to the "effort" required to integrate the D&d3E PH and the D&D3E DMG, or the AD&D2 PH and the AD&D2 CPsiH]. So, frex, making a Dragonlance and a Forgotten Realms product work together (assuming both use the same rules: AD&D2 or D&D3.5E, say) takes no less effort than using the W:tA Axis Mundi book with my D&D3E game--neither takes enough effort to be a significant obstacle.
Which is a long-winded way of saying that there is no one universal standard for "compatible". By the standard of "one from book A, one from book B", i'd consider Everquest RPG compatible with D&D3E books--i could freely mix-n-match bits with no more effort than it takes me to read the two sources. Hell, you're not even guaranteed that any two WotC D&D3E books will be 100% compatible, requiring no effort to integrate (MotP/Epic Level/Dieties&Demigods/BoED, frex).