There has been much talk about the democratizing effect of the web and the opening up of a brave new world of the long tail (the term coined by Wired Editor Chris Anderson), where many small websites can survive and thrive.

However, if there's a long tail for internet ad dollars, it's apparently very skinny: AdAge reports that internet advertising continues to be dominated by its own Big Four: Google, Yahoo, MSN and AOL, much like TV's big four networks. The Interactive Advertising Bureau's analysis of revenue by company size found that the top 10 companies online accounted for 72 percent of all interactive ad revenue last year, likely boosted by MySpace's rise in 2006 and Google's and Yahoo's search ad networks, showing that reach is still king in the marketer's budget.

The Big Four's reach, their expertise in behavioral targeting, not to the mention the labor involved in planning, buying and tracking ads on a host of smaller sites, makes them easy go-to places for marketers to spend their ad dollars.

Ultimately, said Sarah Fay, president-U.S. of Aegis interactive ad agency network Isobar, "anybody who's making a choice of one over the other, they don't have enough budget to do a good cross section."