[mcarvin]

The OP is stating a truism that I agree with (true with all truisms). Google is your default search engine for any query where (you believe) Google offers the highest probability of delivering the intended content/ answer.

So any product, in any vertical, that can respond to a query with greater utility than google - and condition it's userbase that that is the case - has the potential to supplant google for those queries. Great example is the drift of search traffic for flight travel on google to direct traffic to sites like kayak and expedia. (another example is the shift of people search).

The challenge of competing against kayak-like companies that offer great products in specific verticals, will only grow. So if you believe search traffic will not naturally decline over time you are effectively arguing that google will be able to outperform the pace at which new products will be built that have kayak (flight search) / linkedin (people search) / coverhound (auto insurance search) - like potential.

And I think Eric Schmidt would agree. http://www.youtube.com/watch?v=XeIIpLqsOe4

[cynwoody]

Travel search is one vertical in which Google has a serious interest. In 2011, they acquired ITA Software,† which developed QPX, a widely used, Lisp-based airfare search and pricing system. They have since rolled out Google Flights, which competes rather directly with Kayak and Expedia.

†http://en.wikipedia.org/wiki/ITA_Software

[mcarvin]

Agreed. I think that is the point the OP is making. As sites like Kayak grow in popularity, the usefulness of a discovery tool (search), diminishes.