I don't understand what this is supposed to add to the observation that these subjects are important at Google interviews. It seems tautological to refer to interview requirements as "selection bias".

What I meant is that maybe the people working at Google were interested in algorithms even before working at Google and therefore they went to work for Google and therefore they work on algo in their free time. I did not say selection bias, I said self-selection bias http://en.wikipedia.org/wiki/Self-selection_bias