I think it's fair to assume that HN is a fairly technical community and could manage such a feat on its own, so these: "here is how to switch from [insert Google service] to its competitor" posts strike me as karma-bait (and they do get votes). As to these ads you're so troubled by: Twitter ads look like tweets, Facebook ads look like Facebook posts, and of course search ads look like search results, at least in Gmai…
Yeah, those are good arguments to avoid using Twitter and Facebook as well.