I calculate about 128 for the average IQ of a survey respondent who provides one and I suspect that nonresponse means the actual average is closer to 124 or so. (Thus I agree with you that there is a significant gap between the average Nobel laureate and the average LWer.)

I think the right way to look at LW's intellectual endowment is that it's very similar to a top technical college, like Harvey Mudd. There are a handful of professor/postdoc/TA types running around, but as a whole the group skews very young (graph here, 40 is 90th percentile) and so even when people are extraordinarily clever they don't necessarily have the accomplishments or the breadth for that to be obvious. (And because of how IQ distributions work, especially truncated ones with a threshold, we should expect most people to be close to the threshold.)