Well whether there is any benefit to weighting or clamping is definitely record dependent. For perfectly flat records, I agree that there is little or no benefit and in fact a weight can actually dampen or choke the sound a bit. A clamp has no deleterious affect on the sound that I have been able to detect, however. On records that are not perfectly flat, a weight or a clamp helps to bring the record more firmly into contact with the platter and that does two things: It makes it easier for the arm/cartridge to track the grooves, and it dampens resonances in the record itself. So saying they are snake oil is over stating the case.
