The stories shown are determined by user input (upvotes and flags). Moderators tend to rescue stories that are excessively flagged and there's also the second-chance queue, but I don't believe they're actively picking winners and losers on the front page.

Also, the HN global feed is heavily gamed. It's very common practice for startups to organize voting rings to front-page their latest blog post or new product announcement. The simple attempts are caught, but it's common information in the startup world about how to organize group voting efforts to tip a story on to the front page without triggering the voting ring detector too much.

the difference is the incentive (what the algorithm is optimized for). in most of these feeds it’s for ad revenue, hence the results