I think the only thing which will have to change in such cases, is the site's thinking.
If they can increase member retention, they won't have to worry about making the extra $$$ from exit consoles.
On a side note though, as many new popup blockers come out, new code comes out to get around them. I believe it will always be the case, as it follows "If they build it, we will break it down"
I don't think is a very big issue for any serious company.