According to a comment on DigitalPoint forum, Alt tags help some visually impaired visitors who need to use text readers to understand a page format and so should be used. They can’t see the images, but can detect text in ALT tags. In addition to this, they also help you rank better with search engines.
http://forums.digitalpoint.com/showthread.php?t=1627876
The main reason people like the concept of forming an SEO Monopoly is leverage. Traditional SEO is like putting all of your eggs into one basket. An SEO Monopoly is equivalent to owning multiple baskets. The odds of a the searcher finding out about your company or service are much greater if you are running an SEO Monopoly.
