1) "Google shows users what other users like, most of Google's current users favour a small number of major outlets"
This is only partly true, and we have no evidence of it. Google can do whatever they want their results and there are surely other factors. What are they? Why do they exist? etc.. There's room for all sorts of bias in there.
Also, I suggest it's actually not really true either: 'What people want' is BuzzFeed, HuffPo, Breitbart and TMZ. Unfortunately, that's the reality of the world. 'Most people' read that stuff. They want to know what Kim Kardashian thinks about it.
2) "But it shouldn't surprise you that most gas stations mostly stock Coke and Pepsi products."
This is a physical inventory and shelf space problem, google really doesn't have this so much: results can be tailored, represented in different ways, possibly randomized etc..
This situation is a great case for how systematic biases etc. are reinforced.