At the last tech seminar, I asked the guys at Shimano why they used those 'stupid pins' instead of a quick link system. I was told they tested different quick link systems for years and couldn't come up with anything that didn't compromise the strength of the chain by becoming 'the weakest link'. The oversized pin approach apparently doesn't have that problem.

The numbers I was quoted were 'the quick links wore up to 30% faster than the rest of the chain'.