At one time it was true, but at least some of the closed ATI drivers support it too. The open drivers refuse to support S3TC because of algorithm patent issues (the DRI team says it''ll implement it in the drivers they maintain as soon as they know it''s safe to do so). (See Google for the many existing arguments proclaiming the evilness of software and algorithm patents.) If you''re aiming at maximum compatibility with hardware, you shouldn''t make any assumptions about any compressed format support (which means you should store the textures in some format from which you can get uncompressed data).