Yahoo (aka Bing since all their search traffic is handled by Bing at the moment) also spends heavily on acquisition. We (Blekko) did too for a while (although we could never afford to pay hundreds of millions of dollars doing so), there are a lot of people who will sell you traffic. The interesting take away is that search it not nearly so differentiated as it once was. That is hurting CPC (16th straight quarter of declines for Google) and it is hurting loyalty. Lots of people on HN for example use DDG as their search page. That is a huge change in the search business and a source of worry for Google (as the leader) and a source of hope for people breaking into the market. As search becomes commoditized, Ad CPC becomes a race to the bottom. That doesn't bode well for a company depending on Search Advertising to fund multi-billion dollar investments, per quarter, in data centers and other infrastructure.

Its kind of like watching the Pacific ocean erode the cliffs along Malibu, slowly but surely really pricey real estate is turning into tide pools.