I think the problem is one of perception more than anything. Few people like to have adverts and stuff thrust in their face and whenever i land on a site that throws me a popup, unless the website has something totally unique, i rarely go back.
Even worse, those ones that fly around the screen over the text. Even if a site is unique, i NEVER go back to those. I stopped using my favourite site Lastminute.com a while back ‘cos of this and as a result i found latedeals.com which is just as good and without the hard sell 
I wonder how many players get that negative vibe when they hit a casino website, compared to how many actually click the popups. Pretty impossible to tell i guess. Unless you run a survey of visitors in a popup window 