Ok, but what was it that made you think so? I'm sorry if I'm bothering you (and going a bit off topic), but I take a certain interest in the psychology of rule/regulation/law compliance (or the lack thereof)... what I've observed is that it's much more common to think that rules are more restrictive than they are in reality. Racers may know the rules better, but they tend to err the same way.
(By the way, I think I've quoted the relevant class rule before: "One single mainsheet block fitting of any type with or without an integral or attached jamming device may be mounted on the deck or cockpit lip." I read that as "pretty much anything goes".)