The reasoning behind the 100 foot depth limit deals with nitrogen narcosis. 
NASDS is founded on stressing the highest safety standards for the Sport
and that is why they have shallower depth limits (which coincedentally
the Caymans and other areas are moving towards) and shorter bottom times
than any other agency that I know about.
Regarding the depth limit, the incidence of nitrogen narcosis shallower than 
100 foot is significantly smaller than that below 100 feet.  I can't cite 
numbers, but if the majority of divers never experience narcosis above 100 
feet, then they are themselves safer, and one less problem they will probably 
never encounter.
I know people will argue differently, but NASDS is founded on Sport Safety 
for Recreational diving, not for commercial or technical diving.
Beery
 > BM>The Advanced Open Water Certification class teaches night diving, deep
 > divin
 > BM>(to 100 feet as NASDS members don't dive deeper than 100 feet), and
 > BM>navigation.
 > What is the reasoning behind NASDS members not diving past 100 feet.
 > And yes I do know about the physical aspects such as time constraints
 > and nitrogen build up.
 > But just wanted to know the logic as they explain it.
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