I have yet to see any evidence for this and it's a wild accusation that I'm seeing a lot on HN without merits. Occam's razor applies here as well, with the simplest explanation being that search is a difficult problem to solve. And I've written here before that for non-US users at least, Google's results are vastly better than everything else, so it isn't that competition doesn't exist, but hey, you're free to try and solve this problem in a better way.
Evidence would be difficult to offer given that their algorithm is a changing black box.
I also don't see how "search is hard, which is why Google's search results have issues," is a simpler explanation than "Google has some bias towards results that they profit from."
Why not both? Search is really easy if you have a corpus of static information. Search is very hard when you have a huge amount of information that changes, many people are looking for the newest information, and outside influences want to bias search in their favor for profit too.
