It was a member here that pointed out to me what he claimed was the original purpose of the blade on the trigger, with the reduction in unsquare pressures being a side benefit (I too have questioned how useful it actually is in that regard). I thought about the fact that I've seen tabbed triggers on a number of bolt action rifles with adjustable pull weights (i.e. Savage's "Accutrigger") and that plus the explanation made sense to me. I doubt Glock was the first person to use this system, but whoever did was rather clever.