This looks like an accident. Even many of the suspicious sites that do it seem to be an accidental side effect. The ones that annoy me the most are the news articles that trigger a history event on scroll. I think they do it as part of a tracking mechanism to detect scroll position, but the result is you have to press back twice to leave. I can't see the benefit, not like anyone is going to press back then say, "oh i guess i can't leave so I'll click an ad".