I agree. Getting listed on web hosting directories is the least expensive and one of the most effective ways for hosting companies to promote their plans.

It is a very targetted marketing to visitors that are already searching the web to buy hosting plans.

This best practice is same for many industies just like hosting sector. It is always benefitable for companies to advertise at places where people came to search for what they are selling for.

Advertising on search engines is much more expensive in most cases I think.