The ide interface is limited to that, but scsi.device doesn't ignore values above that. It will work fine until a single transfer is larger and then it will fail. So you might not notice until a large file is loaded into ram.
Actually this is not the entire truth. The problem is not a bug in scsi.device. The problem is the age of scsi.device and that the ATA specs have changed since scsi.device was written. Scsi.device relies on a feature which is not present any more in the current ATA specs. It does not have problems with old drives. Only with new drives the MaxTransfer problems occur.
