If Google doesn't figure out how to move beyond search ads, Rohan said, the "law of large numbers" will inevitably shrink revenue growth, probably down to the 30% range.
Rohan made his comments moderating an OMMA Hollywood debate about whether Google will emerge as king of all media. While no one doubts that Google plans to extend to TV, radio and other types of ads, opinions vary about whether the company will be as successful in more traditional media as it's been with search.
Stock analyst Henry Blodget argued that Google can't sell ads as profitably for TV or radio as in search engines, because, in part, Google doesn't own or control that content. With search, by contrast, the "content" is the results page itself -- and while Google doesn't own the Web sites that appear in those pages, it's the technology that generates them.
Taking the pro-Google side, Kevin Lee, chairman and co-founder of Did-It Media Management, said that Google potentially can make TV or radio ads more relevant, which will do a lot to increase the value of advertising.
When asked how many of his current clients were using Google for anything other than search ads, Lee said that about half of his largest clients were experimenting with Google for non-search advertising -- mainly through Google's networks.
Aside from TV and radio, Google also has ambitions to extend into in-game advertising. Just this week, the company confirmed it purchased game ad tech firm Adscape Media.