It sounds like you think that the reported results of these A/B tests are snake oil, not A/B testing itself. I think most authors of A/B-testing-report articles would recommend testing such changes yourself, as opposed to accepting their findings as fact for every site in existence. Those who said the popup forms did not work for them only know that because they A/B tested them.

I think a healthy conclusion is "this worked for us, so it might be a good idea, but you should test it for your site". Wouldn't you agree?