Many of the popups display advertisments, which is a method the web sites make money. I find them really annoying and usually ignore them. There are better ways to make money than send many popups to a visitor.

__________________
Confused about technology? Technically Easy has the answers!

How I Converted from Blogger to WordPress
Do You Quit Too Early?
Using Google Alerts to Track Copies of Your Web Content
Viewing Your Web Site in Many Browsers with Browsershots