i would say people go to a certain pool not because of slightly better variance but because of a better web interface.
My opinion is that a rather significant percentage of hashers are actually really bad at mathematics (which is why they are mining at a loss relative to simply purchasing the bitcoins directly).
As such, they don't understand variance, or how pools reduce variance. Instead they just assume "bigger is better". They figure that the largest pools must be the best pools, relying on the idea that enough other people have done the investigation as to which pool is best and therefore by going with the majority they are benefiting from the research of others (just like people who aren't very good at computer programming assume that enough other people have already reviewed the bitcoin source, so they choose the wallet that they believe most people are using).
Furthermore, because larger pools get blocks more often, many of these hashers believe that more blocks = more bitcoins, and therefore think that larger pools will earn them more money.
